As Twitch mentioned, the 2610 will make a good Frame Relay switch.
If you can pick up a nm4-a/s for the 2610 that would work well. The nm4-a/s has 4 serial ports in a single card, so you can then have 4 routers plugged into it using back to back serial cables. You can pick the cards up pretty cheap second hand.
Hope this helps,