Sleeping Bags - Antigua

Try Old Town Outfitters. Won't be cheap.

Otherwise, hit up Miraflores Mall in the city. The camionetas (chicken buses) going to Guate stop outside of it (though as of today they are currently on strike AFAIK).

Old town had them before but not sure if they still do. And like enroutesiglo said, they'll be expensive.

Another poss: North Face in Oakland Mall (Zona 10). I know I saw one other outdoor-type store in there too, can't remember the name. You can get a taxi directly there from Antigua for as low as 200 if you bargain, and 200 easily coming back... or pretty easily by public transport.

walmart has sleeping bags

I was in Cemaco several months ago (across the street from Walmart on Calzada Roosevelt). They had sleeping bags and other outdoor gear. It looks like a small store from a distance, but it is a very large store on two floors. From what I remember, they carried a lot of home products but little to no groceries. Maybe hit up Walmart first and only go across the street if you want to compare.

I am not bashing Old Town. Maybe for the brands they carry, the prices are ok. Like others have said, though, their prices are very high. Oakland Mall is very high priced, too. However, again, that may partly be due to the particular brands they carry. I suspect the store rent is pretty high there, too.

As far as the local markets in Antigua, Chimaltenango, Guatemala City, etc., I don't ever remember seeing sleeping bags.