The part number is A05342, but I have no idea how many links it has. It is possible that the number of links shown in the part list illustration is correct, but I wouldn't bet on it:
![[Linked Image]](https://www.outdoorking-forum.com.au/forum/uploads/usergals/2014/07/full-2772-17286-rover_colt_8_3_speed_drive_chain.jpg)
There is a guy on ebay selling a chain that fits "selected" Rover Colt mowers - you could count the links in his picture:
http://www.ebay.com.au/itm/GEARBOX-...mowerAccessories&hash=item27dd6f235b(I think you'd need to contact him though, to establish which Colts if fits, and whether it is the right length or he's just counting on the buyer shortening it if necessary.)
Failing that I think the most practical solution is for somebody who has one, to count the links.