They use their own threads, and since they're such old markers you'll have a hard time finding any other barrel than the stock one. The only aftermarket one I've heard of is a J&J ceramic, but i doubt you'll be coming across those any time soon.
If you dig around the pump section, I remember someone saying how they'd changed the thread to fit spyder barrels and would do so for others for a small charge. Then you'd just need to find a spyder barrel that is thin enough to go through the pump handle, but that's only if he'll do it for you.
You're against the odds. Best of luck though.