Eminence has some very nice speakers. Check out the Patriat and Red Coat series. I've got a could 12" Governors and Wizards and love them both. As for them being made in America, currently they are, but they are getting ready outsource their OEM type speakers and such to China. Their main aftermarket speakers will still be made in the good ol' USofA :) . They have great customer support from my experience as well.

You might also want to check out Weber speakers at tedweber.com. Ted is very helpfull in making suggestions for your replacement speaker.

The only way you could substitue a 12" speaker for a 10" speaker would be if your cabinet were big enough to make the opening larger. This is more than likely not the case, so just stick with the 10". There are some very nice ones out there.