Even if they're there, I don't think you can use them unless the PSP itself validates the purchases. Which I'm not sure if it does when you connect your PSP to your PS3. It's not like transferring a picture or demo, these files need to be authorized for use, otherwise anyone could just connect their PSP to your PS3 and download what you have. I've never transferred files from a PS3 to PSP before, but just from using DRM restricted files, I'd assume it's the same process. Like with iTunes, if you downloaded a DRM restricted song, you can transfer it to another computer, but to play it on that computer you have to authorize it. Same with these files, you most likely have to authorize your PSP to use them, which requires a wireless internet connection to sign in. Unless you can do that while connected to your PS3. Have you thought about using Media Go on your computer? You could try transferring the files that way and see if that helps.
Even if you tried to update the catalog, that's done in game, you can't download that off the PSN store. So I think you really need a wifi connection for any of these methods, I don't see a way around it. I have no idea where you are located, but if you go around town searching for networks, you can probably find an open one to connect to. Starbucks and McDonalds are perhaps two places you can leach from since almost all their stores offer free wifi, and there are generally a bunch of those the world over.