I do not know of one to make an Alliance style bow. The easiest way to do it though:
Get a piece of 1/2 PVC pipe. Cut to length. mark out where you want to make the bends. Heat that area up either with a heat gun (easiest way) or very hot water (can work but difficult). Bend gently into shape (don't want to fold the tube).
Here's a video about how to bend PVC piping with a heat gun - things to know/think about -
Here's a video of building a functioning PVC bow. Ignore the flattening/tapering/stringing bits but if you want to see some bending techniques.