LocostUSA.com

Harada Shokai supplies Weber/Solex kits for several Japanese engines.
They can even supply the Webers but I doubt that would be price competitive.
Site is in Japanese but web based translation worked well for me.

So here is an option to vastly simplify use of Japanese engines.
Webers and stand alone ignition rather than fighting all the extra from an original wire harness.

http://www.jcy.co.jp/hrd/
Email is hrd#gol.com (You have to replace the # with @, I guess they despise SPAM too).

No affiliation but I may buy one of their intakes for a Miata 1.8.

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If I must be a one-man PC free zone, so be it!

It turns out that Jenvey do list manifolds without their very $$$£££ throttle bodies.
Here is a direct link for Miata, https://store.jenvey.co.uk/manifolds/mazda-manifold
I find their site a little awkward to navigate but they do have a wide selection and the exchange rate is not horrible right now.
About $250.00 and shipping for the stripped Miata manifold.

None of the U.S. companies appear to have manifolds without making you buy a whole ITB kit.

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If I must be a one-man PC free zone, so be it!