I order most of my stuff online unless I need it right away. I can say for me, usually finding what you want and simply searching the part number on a good internet search engine works out well.
Then of course, I look around at the best priced sites for some coupon codes, specials, etc.
It just depends on how much time I have.
I've gotten a hitch from RVWholesalers parts section and it was the best price within $100 or more. As for some other things, I have found adventurerv.net has good prices and also rvupgradestore.com.
It just really depends. If it something small, I have found that I can do just as well at my local dealer. For example, broken plastic latches and things like that.
Good luck but, like I said certainly searching the internet search engine with the part number is a good place to start.
2012 Keystone Sprinter
Still sticking around for the good people and advice.