If you post the actual model number of the transmitter and receiver it will help determine what might work. The picture below is a partial listing of discontinued Futaba transmitters so there are many variables.

There are always exceptions, but, most servos will work with most receivers. If your servos have the Futaba "J" connector they will plug in to a modern Futaba receiver with no issues. If they are old enough to have the "G" connector (discontinued in 1991) you can cut the connector off and replace it with a "J" connector. I've heard of adapters to connect G to J but have never seen one. Unless an old G servo is something really great I'd replace it with a new model.
Info about G connector http://www.futaba-rc.com/faq/product-faq.html#q20