you just want a common brown garden snail, sometimes referred to as European brown garden snail. there are predatory snails that have a piercing mechanism. ime, local gardening clubs, are more than happy to help you identify, and even offer specimens (they are considered a pest by gardeners, i wouldnt tell them you plan on breeding them)you can find most of what you need to know about them here;
http://entnemdept.ufl.edu/creatures/misc/gastro/brown_garden_snail.htm
they can easily be bred in a 10gal with a leaf litter bottom, ime within 3 generations(place each new generation in a newly sanitized tank), pesticides and pathogens are usually down to acceptable levels.
blue or green bottle flies are also an excellent feeder and a xanth favorite, either as maggots or adult flies, also easy and fast to breed, and probably the best xanth hunger strike breaker.
recommend sticking to relatively smaller feeders, and avoiding crickets whenever possible, especially petstore ones
if you want flies, just breed your own, imo, bait shop maggots are best avoided (they are usually raised on a large dead animal inside of a barn imo, increased risk of coccidia), but there is certainly nothing wrong with buying them as starter culture (again 2-3 generations before use as feeders) although buying them is really not necessary.
even though i am not currently keeping xanths, i still raise flies sometimes, for kokanee fishing (landlocked sockeye salmon) and also for mantis. search my recent posts for more info on fly raising, another great and easy to raise feeder is black soldier fly larvae. ill post links if i get around to it. btw there are vids on you tube of how to raise most common feeders, there also used to be a vid from cf member kenya, of a xanth eating a garden snail.
and dont forget the old stand by , dubia. jmo
Quite gross I think, but if it keeps the little chap happy then I'll feed them to him, but I won't be able to watch! 
