Just go here...
http://www.mcmaster.com/#urethane-casting-compounds/=p06yln
Break down is something along these lines...
OEM feel, Durometer of 60A, p/n: 8644K24
Performance, Durometer of 80A, p/n: 8644K11
Race, Durometer of 94A, p/n: 8644K18
For more information on the durometer scale you can read about it here,
http://www.mcmaster.com/#about-rubber-durometer-hardness/=p070uf
1lb will be almost enough to do two, but I'd order 2lbs worth as you really need about 1-1/2lbs of material to fill both the front and rear roll resistors. All of the p/n's I listed also cure to a black color so it will look like it belongs as opposed to the amber color that that other website indicated. Plus that site didn't list prices. McMaster is reasonable priced at $33 a pound.
EDIT: This assumes you are removing the existing rubber material in the roll resistors. If you leave that rubber in you will not need more than 1lb. However removing the existing material is recommended.
I also found this website too,
http://www.energysuspensionparts.com/proddetail.asp?prod=DIYMMI They are selling the same product as McMaster. If you do not know what you are doing they also have instructions for you too, which are here:
http://www.energysuspensionparts.com/About-How-to-Make-Universal-Motor-Mount-Inserts.asp
In all cases the product comes from Forsch Polymer,
http://www.forschpolymer.com/index.html