I should think a classic Dow-Key relay, such as the DK-1, would do the job. Granted they are no longer manufactured, but neither are the rigs that they are commonly used with. That said, they aren't difficult to find on swap lists or eBay. Just don't pay an arm and a leg. They are available with a host of relay voltages, from 6v DC all the way up to 240v AC. The most common ones have either a 117v AC or 12v DC coil. If you purchase one, make sure the coil voltage is appropriate for your application. Many vintage transmitters have a tap on the rear to provide voltage on transmit expressly for operation of T/R relays. Many Dow-Keys have an external pair of contacts for operating a linear, muting, or any other function that's convenient when transmitting.
EF Johnson made a T/R relay similar in function to the MFJ model, but much larger and capable of 4KW. It was tube-type. These are rare and expensive. The model # was 250-39. See a picture here: http://antiqueradios.com/forums/viewtopic.php?f=5&t=170170
See a nice collection of Dow-Keys here: http://www.n4mw.com/gdowkey.htm