Just the crossmember? I don't think any marketed on a stand alone basis. There are a couple belly armor systems (e.g. Savvy Under Armor) that incorporate a new crossmember. You could always contact them and see if they'll sell you just that (and presumably the transmission mount to go with it). Although note that most of those raise things up materially and so that may create other issues you have to be prepared to deal with. For example, makes drive line angles more extreme.
There are few people around here who have built their own crossmember. Might try doing searches in the build threads.
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