This thread is for expressions of interest - I don't have anything to sell, yet.
I'm looking into making up reproduction seat bases for these bikes. They will not be 100% as-original, concourse-standard, but they will be strong, good quality, well-fitting parts.
They will also suit DTs with some frame mods, and the YZ125A (not sure about the YZ250/360).
Cost will be minimal - enough to cover the cost of materials and a slab of beer for my fibre-glassing guru mate. Call it $50 each as a starting point - and the more that are made, the lower the unit price.
If you're interested, let me know how interested you are (and let me know which type you're interested in), and I'll keep you in the loop.
ETA is a month or two, but could be quicker if you need it sooner.