There are hundreds of dealers.
You need to find a good one. Google and your phone work great!
Most do more with electric beds, tap turner oners, walking frames, etc and powerchairs scare them to death.
In the case of many makes, including Sunrise Medical, as I regularly need, Clarkes are OK usually and will ship straight to you.
http://www.clarksmobility.com for example. I used many dealers though. Some are good some less so.
You can get prices and part numbers directly from Sunparts Online for Sunrise Medical stuff with the password and user name of "guest" and "guest" here:
http://parts.sunrisemedical.eu/uk/login/login.php For all sunrise UK stuff... Remember you dont pay VAT!
But if you order a wrong part via a part number via a dealer its your own problem...
There are similar sites for other manufacturers or downloadable pdf files with part numbers in.
Its a pain to find them but they
are available!
If you know of any good dealers or parts pdf files or websites post them in this stickied thread!
I built (redesigned) 3 complete Powerchairs this way. Ordering control equipment from
http://www.pgdt.com and wheels and tyres and bearings, metal, rose joints, stainless bolts etc from
http://www.ebay.co.uk and elsewhere on the web.
You just need to understand exactly what you are looking for! And what else it is used for. Wheels and tyres are used on minibikes, quad bikes, etc. Or scooters. Bearings and rose joints are used on almost everything. These sorts of parts are common and not wheelchair parts.