For those Paraguay RPCV who, like me, were unfortunate enough to break the glass flask in their mate thermo, do not despair! The website latinoyes can come to your rescue! I can tell you from personal experience that their replacement glass flasks fit any normal Termolar termo. The photo (on their website) makes it look too short, but it dose in fact fit the normal 1 liter matero termo size. Also, if your running low on your preferred marca of tereré yerba, they also sell Kurupi, Campesino, Pajarito, Selecta, Colon, etc.
Their prices are moderate, and the shipping cost was reasonable. The package arrived very fast and in good condition. Overall I am very pleased with the site and happy that I have found a way to continue my tereré and mate habit in the States.
EDIT: A friend sent me a link to Go Yerba Mate which has Paraguayan yerba as well and some very interesting tereré equipo for people on the go. They have a large selection of guampas too. So it looks like there are several options out there!