tea tins as alternatives to mason jars?
Positively not for long term storage. For the ounce or two you've got in your rotation that you're into regularly, if the seal is good on those tea thinggies, sure, why not.
Wal-Mart, eBay, Amazon. Screw-top canning jars are all easily available, in whatever size, normal or wide mouth, from any of these. I use 8 ounce regular Ball jars = Case of 12, under $8 from Wal-Mart.
Oh and wherever you live, whatever the ambient humidity and temperature, it's important to keep pipe tobacco out of the light, and in a relatively cool place (ambient temp of under 75 F.). We use canning jars, so unlike cigars, the ambient humidity don't matter in the least since it won't affect pipe tobacco in a sealed canning jar.