only stores i can think of would be M&Y, Pacific Angler, Riverside......basically the fishing exclusive shops. big box stores will only have the flies they can order overseas and lets face it Intruders take time to tie (up to an hour each) so they can only get your basic type ones like the Hobo spey, Pick yer pockets and a few other styles. I know that M&Y and Pacific Angler buy from local (ish) tiers because the demand is there but these flies will run you like $5-$9 per fly and even up
OR you can take up tying and the many hours it takes to learn techniques and such, all the money for materials and then tie your own. Do you save much money in the long run............probably not but us that tie flies like to think we do
plus its really enjoyable to catch fish on something you tied especially when you create/customize your own patterns