Lift support cross reference

Can anyone tell me where to find a cross reference catalog for lift supports? The SPD ones on my fiberglass tonneau cover are shot and I can't find the same nor can I find a cross reference to get new ones. Tried the auto parts stores and I get a stupid look, tried online and nothing. Please help - cover is heavy and getting old quick.

You might look here htt
p://www.monroe.com/products/mp_detail.asp?cat=Accessories&detail=Max-Lift
noticed they have a tech support line, they probably can help you.