For most battletech models you don't you don't need to assemble them. They are single piece plastic.

As mentioned, the hunchback 4G is in the Inner Sphere urban lance force pack.
https://www.amazon.com/Catalyst-Game-Labs-BattleTech-Force/dp/B09NDQ3S3H

You can pick it up from Amazon, multiple other online shops, or your friendly local game store (FLGS) may carry it. That will save you the shipping.

There is a kickstarter for more minis going on right now, but delivery dates are ~1 year away.