I'm new to the Fox scene, and don't really know where to look since everyone caters to the 4.6 boys now.
I buy the majority of my performance parts from Summit Racing and Brothers Performance. You can get a 5.0 Magazine or Muscle Mustangs & Fast Fords for a ton of listings.
You've just gotta look is all... and not very hard IMO. There's like a whole bazillion site and companies that make performance stuff for the 5.0... probably anything you could ever want/dream of. Steeda, Vortech, Summit Racing... the list goes on and on. I love the Summit catalog since it gives you an idea of all the manufacturers out there. Good luck, and welcome!
easy doesn't fully encompass how quickly you can find parts but if you don't like ebay for whatever reason-Summit and Jegs are good ones to go though, LRS (latemodel resto; www.50resto.com) has a few one off parts...there's tons of places that carry 5.0 parts-from what I've seen, the mod motors are definitely a craze, but the amount of parts available is still in the 5.0's favor, remember the 302 was in production from 1968-2000...there's more places and people that make parts for those engines than you can shake a stick at...seek and ye shall find!
If you wanna get the parts you want/need for the BEST price ..... you'll end up using at least 10 different suppliers. Once you figure shipping in from alot of companies, you'll realize that sometimes, "$20.00" more for the part isn't so bad afterall.