Elsewhere I've traveled the stores carrying the Tax Refund forms are hit and miss. The larger stores that get a lot of tourist traffic would have the forms on hand but the smaller ones are a hit and miss.
Normally the signature of a Border Control officer is not required since most places the refund is given at the airport.
For Example Tel-Aviv Airport has 2 locations where you get your refund and all you need is a check and form, which you can obtain at any store or at the VAT refund counter itself.
In Canada at the land border crossings the Tax Refund was given at the Duty Free Shops like IGL and the form to claim the refund can be obtained online.
Europe on the other hand may be different. But in Austria for example you can follow this site to find where the locations for refund are and the same one in Switzerland.
Additional Information about VAT refunds from Zurich airport. You can take a look at the map for where the Customs are located. One thing they might be asking from you though would probably be a boarding pass, so I don't know how you would be able to get back to the store afterwards.