sproggs speedster car seat

iv just brought a sproggs speedster pushchair but havin big trouble findin a autofix base for the car wat is permanetly strapped in, dint know if anyone got any idea of wear i can buy one n how much, the lady in the shop were we purchansed wasnt sure if they ever made one which will be a big pain if they didnt cos i have a three door car and a 3 yr old to strap in aswell.
any ideas people
thanks