Hmmm... They sell harlys at Petsmart and Petco around me. Ask if they can order them for you. They are normally about $2.50 each. I got mine on sale for about $1.25 each.
You are correct about the BN pleco.
Gouramis eat the same stuff as other fish. Just make sure that the food gets too them. My dwarf gourami doesn't come up for food, while my harlys, glo fish, and guppies are all over it. My neons also hang down. So, I just look for which side of the tank the gourami is on, then feed on the opposite side for the harlys, etc. Then, I put the flakes into the water, submerged and they gently float down. The neons see it and dart over, then whatever they miss, a far amount, the gourami gets. Finally, the food at the top is gone, and the guppies and glofish go scouring the rest of the tank (bottom) to pick off any remaining flake. The cories get shrimp pellets.