I don't like bike shops with " attitudes !" I tell them so before I leave & never go back. They are running off a potential future customer who may want to buy one of THEIR bikes.
That said, there are plenty of 27" tires on the market at different prices. Below is a link to just a few. Other retailers will have some too.
http://www.niagaracycle.com/index.php?cPath=131_167
I would , or have someone, disassemble & check the tubes, inside of the tires, rim strips, & rims to look for anything causing leakage or damage to the tubes. Then properly mount the tires. You have gotten good advise from others above as well. You do need to learn how to do this ,yourself, if you are going to ride a bike.
By the way, I live on rough, limerock roads & have ridden old Schwinns, etc., bikes all around here without ever having a flat.