Suitable forms of elastomer for replacement in suspension?

[LittleSkink]

This is a question about suspension seat posts but could equally apply to other elastomer based suspension items I guess

Just replaced an old elastomer based suspension seat post with a new spring based one - main reason for the change is the elastomer has gone hard and crumbly, other than that it is in fine fettle

Any suggestions for a replacement material? I need c100mm x c16mm diam but its a closed tube so different shapes could be made to fit, eg if it came in sheet form I can cut discs