I think the problem at JCPenney's may have been that you asked for a boy's "First Communion Suit" - and that may have thrown the sales staff. It really is just a boy's suit, unless you want a white suit.
I think if you shop just before Easter at any number of department and children's stores you will have better luck...and best of all, you might find a suit on clearance just after Easter.
If you want a white suit, (less common, but not unheard of) check with a tuxedo shop or bridal shop for rental or purchase. You might even consider renting a suit, white or dark, if the price is right.
Maddle