Seems like everyone forgets a rigging gage.
The best sorce for a complete starter set of saddle building tools can be found in the Stolhman Saddle Making Encylo. Vol 1 and 2. Also includes plans for building what can't be bought.
I find "Old George" to be invaluable for tooling swells. I believe there is an articulating draw down stand that can be had for a very high end substitute.
I made my own chinaman, smashers, welt jigs, ground seat jig, rigging gage and many more that I can't think of at present.
I modified many existing marketed tools, and found a lot of stuff at flea markets and used tool outfits that can be reworked to suit a need.
Being a fabricator by day time trade does help. My machining skills have served me well in tool making efforts.
I would highly recommend the Stolhman books to anyone just getting started.