As above - the 3-button fob works the same as the two button one, the boot button will simply be redundant when used with a car with the earlier Pektron SCU set-up. The two button ones have been unavailable from XPart for several years now, and XPart state to use the 3 button version istead.
You could have a look on eBay as an occassional one does pop up on rare occassions. Otherwise contact technozen via this forum, or his website (http://www.technozen-electronics.co.uk/
), or you can get one from any XPart agent (but it will be £106 + programming from them).
Assuming you are in Europe, you require the 433 MHz version, part number YWX000360.
If buying from eBay, take care that the fob is indeed new/unused, and has the original barcode label on the bubble pack - you can't get it programmed without it. Also take note that it is the correct frequency - some markets used a fob with a 315 MHz frequency, which of course won't work with a 433MHz system.