Either cut the factory 1.1 SPI manifold and weld a flange to it (difficult weld and very prone to cracking), or build / weld up one from scratch. Otherwise look for used ones on here, FB, ebay, etc.
In my opinion, you can have one or the other. Very rarely have I seen something so specific be good quality and reasonably priced. That is my own opinion, but like woj said, trawl tinternet for something or save up for a good quality one.