Emy.e and Mod podge

Hey Emy.e, I have exactly the same problem! (only I'm in the UK)
Google kindly told me that mod podge is just a trade name for PVA made specially for decoupage (or something like that). It also comes in different varieties such as matte, glossy and sparkly finishes. You could probably replace it with any brand of PVA-containing glue, or maybe fabric/tacky glues depending on what you're making. For example, I'm currently trying to make a version of the mod podge shoes project for prom and I'm using random fray-stop glue on the ribbon straps and some other random tacky glue to cover my shoes in the fabric. If you're doing a project where it calls for mod podge to finish the thing off by kind of lacquering it then I guess any clear-drying glue would do (but I'm sure other people know more about it than me). And if you're doing DIY screenprinting, I'd have thought replacing the mod podge with any waterproof glue would work, because you're only trying to stop the paint leeching into places where you don't want it.
Sorry about the slightly exhaustive answer... If you're really stuck, you could always ask someone in your local craft store, I'm sure they'd be able to help more than I have!