In response to your question there are very few companies worldwide who can actually provide a broadbased service for wheelchair users such as you seem to be seeking. The majority of specialist tour providers are based in the USA (5 agencies), Canada (2 agencies), UK (1 agency and around 4 holiday/vacation based tour operators), Spain (my company Disabled Accessible Travel), (Italy, 2 agencies).
The key issue for you is that most of these agencies specialise in cruise vacations or resort based vacations, NOT individual services for parts of travel such as just an accessible airport transfer or just reserving a hotel room with roll-in shower. You mention Italy so you have either been in touch with Accessible Europe or Accessible Italy, Accessible Europe will be able to assist with Italian based services and also Asia through their other accessible travel based company.
My own company, Disabled Accessible Travel offers a unique bespoke service to wheelchair users and we are happy to supply full or part services where they are possible in any one of 51 countries where we have suppliers. Feel free to email firstname.lastname@example.org with your requirements. We are based in Barcelona, Spain.