That's why the MTN-MAXlp was created. There wasn't ever a 17mm buck driver that would do more than ~1A and still fit in a P60. There was also a lack of high-powered buck drivers that could fit in 17mm lights like the UF-1405.
If the price is too high then you can just get the PCB and build your own. I posted the PCB, parts required, etc., including the board needed to program the MCU on this forum. Here is the post that will tell you pretty much all you need to know.