Where to buy basic clothing items? (Asunción)

Hi All - Just arrived the other day and am looking forward to exploring Asuncion!

First order of business, however, is to find somewhere to buy inexpensive undershirts and some casual short pants to tide me over until my lost baggage catches up to me. Any suggestions?

Is there a store that's analogous to Costco or JC Penneys that sells decent and inexpensive basics? Alternatively, maybe a sporting goods store?

Many thanks for any and all advice!

Cheers,
Rob