Bondstone- I assume this is a concrete product (split dyed concrete blocks) that "resembles" stonework. The nearest thing to it available now is probably "Hallmark" made by Roadstone. I think in this instance you'd be very foolsih to try and match a finish like this- firstly: you won't be able to source the material (probably), secondly: colour and shade variation is inevitable even if you do and thirdly: architects/ designers will probably use another material altogether rather than try and match an existing finish. Depending on the design you could make a feature of your extension using a complimentary or contrasting finish. Have you considered white sand and cement render (looks great and is very popular), wet or dry dash (enjoying a resurgence in popularity) or timber sheeting (cedar wood or others) or brickwork (brickwork laid in white sand/ cement looks far supeior to the normal portland cement mix).