To answer your Question(s) briefly...
...will they already be sold out?
That is a hard question to answer definitively, however, almost certainly not for all services as 当日券 [same-day tickets] are sold. During peak periods, 立席特急券 [Reserved Standing Tickets] are available for Hokuriku/Tohoku/Akita Shinkansen services however the Tokaido Shinkansen (Tokyo - Shin Osaka) does not have that option available.
＊ 当日券 [Same-Day Tickets] Require purchasing at a JR Midori-no-Madoguchi however in peak periods expect to wait over an hour. The Tokyo Station waiting lines during rush seasons can be up to 3 hours.
＊ 立席特急券 [Reserved Standing Tickets] Are Only available on Hokuriku/Tohoku/Akita Shinkansen services only for Car 4. They are only sold when all reserved seats have been booked.
Should I forget the JR pass and just book a Nozomi train instead?
That depends on your travel.
Is the sum of all your rail travel in Japan
1. on mostly or totally JR services?
2. equal to or greater than the price of a JR Pass?
If the answer is NO to both of those questions then it will be cheaper to go without the Rail Pass (however if you are planning to catch the Shinkansen return to Kyoto, then it is almost certainly going to be cheaper WITH the pass).
Will that open my options a bit?
The Nozomi Super Express is the fastest Shinkansen offered on the Tokaido Line Stopping at Tokyo - Shinagawa = Shin Yokohama - Nagoya - Kyoto - Shin Osaka (and sometimes continuing on to Hakata). If time is your enemy it may open up an hour or two but otherwise your options shouldn't change.
Finally, can we book the reserved seats from the JR office at Narita?
The JR みどりの窓口 [Midori-no-Madoguchi] is open 6：30 ～ 21：45 and is able to process reservations for any JR rail services throughout Japan.
In more depth...
The Obon season is usually the busiest time for travel in the Japanese calendar.
Shinkansen are regularly filled past capacity (with special Reserved Car Standing Tickets) available for purchase on each respective day) and Free Seating cars normally have an hour if not longer wait to board (as the cars may be unable to accomodate all the people in the lines for each timed service).
It is suggested that you purchase tickets in advance through either a friend or travel agent. There are reservation systems available, however they are in Japanese and require both a Japanese address and Japanese form of payment.
Note that Shinkansen tickets are sold from one month before each scheduled service and in the cases of Obon usually sell most seats within the first 3 hours of reservations opening (as discounts are offered if purchased through JR online systems).
If you are going to try your luck with the Free Seating car (good luck), a tactic I use often is to wait in line to Car 4 of the Nozomi (or the adjacent Reserved Seating car to the Free Seat car of any other Shinkansen) and cut inside the carriage to grab a seat. This wont win you friends but it usually gets you a seat.
Note that you can still book Nozomi Trains with the JR Pass, however you will need to pay the Express Fee (Your Distance Fee will be free as it comes out of the JR Pass).
Checking Seat Availablity
Seat availability can be checked at the following website
JR Shinkansen Seat Availablity - Japanese
The website is in Japanese, however using is as follows.
Month | Day
Hour | Minute
Departure Station | Arrival Station
For the Shinkansen Name you will want either the first or second option.
- のぞみ・ひかり・みずほ・さくら・つばめ [Nozomi - Hikari - Mizuho - Sakura - Tsubame]
- こだま [Kodama] (Stops all stations between Tokyo and Shin-Osaka)
For the Departure Station you will want the 1st choice.
And for Arrival Station you will want the 16th choice.
Then click the button the the right 検索 [Search]
The next page will show a table as follows.
Empty Seat Information | Normal Seat | Green Seat
Service Name | Departure Time | Arrival Time | NS Seat | S Seat | NS Seat | S Seat
eg. Nozomi 25 | 10:30 | 13:06 | 〇 | ＊ | 〇 | ＊
NS : Non-Smoking, S: Smoking
A 〇 denotes seats are plentiful.
A △ denotes there are fewer that 30 seats available.
A × denotes there are no seats available.
An ＊ denotes that particular car is not available on the service.
The information on this site is updated live with JR servers and is accurate to at least 5 minutes.
Although you didnt state it, you may wish to consider other options such as Highway Bus, LCC / standard Air travel or even 特急 [Express Trains] (This may be up to a 6 hour trip between Tokyo and Osaka) should you fail to get the Shinkansen tickets that you want / as a back-up plan.