Filters don't require a RX to purchase online. Check out EBay for filters and replacement mask parts.
Mask replacement parts do not require a RX either. This is how EBay sellers get past the RX requirement.....they piece out the masks. You can order filters and replacement parts from cpap.com our forum host if you want to.
The whole mask package does require a RX though but replacement parts don't. You can buy the replacement parts individually and put your mask together. I know it doesn't make sense but that is the way it is.
If you have a primary care doctor then he could write the RX...doesn't have to be a sleep doctor specialist.
Ebay often is a good way to build your own mask. Just depends on what mask you are using. Mostly it is the most commonly used masks. I have seen filters on EBay for most machines even the older machines at very reasonable prices (for cpap stuff anyway). I have used EBay for filters and some replacement parts.
Which mask do you use?