RM250 Shock Question

I am looking to buy a 1985 rebuilt rm250 for about $400. The problem is it doesn't have a rear shock. Does anyone know what other shocks would fit this bike. Different year rm250's or how about a shock from an rm125? All comments appreciated.

Bump for help. A 1985 rm125 shock would fit a 1985 rm250 right? Also, I am a newbie and curious what the socket looking thing is for on a dirt bike shock. The one's I have been looking at have a cable/hose attached and I have seen others that are molded to the mounting of the shock.