Hi dr_st and USSS,
Many thanks for confirming docking station compatibility!
1. For everyone's information, we have used the "ThinkPad Mini Port Replicator Series 3 (Product no: 4336-xxx)" [the 2nd item in below link as you folks supplied]:www.thinkscopes.com/2012/11/10/thinkpad ... replicator
2. From personal experience, our T410 and X230 were fully compatible with the "ThinkPad Mini Port Replicator Series 3 (Product no: 4336-xxx)".
From deduction, one would imagine that the X220 would also be compatible with above Mini Port Replicator Series 3.
Thinkpads like to plan their Port Replicators to be compatible for several generations.