Bought my first two guns at a Coast to Coast Hardware store. Now the store is out of business and the local Tru-Valu and Ace Hardware stores stopped selling ammunition about 6 or 7 years ago.
As for OP I should have mentioned that modern chokes are built with a longer taper than some of the old chokes we had so they can handle steel shot.
Nobody can tell you what your gun can and cannot shoot well without you trying it. the manufacturers suggestions give you a good start but every gun is a law unto itself and what shoots good in my gun may not shoot good in your gun even though they both may be the same choke size and gauge. Even your choice of brands and types will affect you. Buy a few boxes in different load weights and sizes and brands and find out what you and your gun like the most then remember it, mark it down, tattoo it on your forehead so the clerk can read it..............no scratch that last, if it isn't in text speak and the clerk is young they won't understand it.