Where do you plan to go? Mexico, Canada, the Caribbean, and Hawaii are not considered international as far as jumpseats are concerned. To answer your question only AS, CO, DL, NW, UA, US and FedEx are on our international jumpseat list. Sorry.
I'd say try Sun Country, but......
Perhaps you can find out who is servicing their HMMTF/Mark Travel contract to Costa Rica (if they still are doing it). Imagine it is ATA or Champion.
Dont know the latest with Continental, but a few years back, "officially" you had to be on the International Jumpseat list, but EWR/IAH were usually cool about letting you on, and letting the captain be the judge. Be ready to spend a little extra time in SJ, and worst case, you might have to buy a ticket home. I never had to, but was afraid it could happen.