What version do you have? I don't see that this has been updated since V42. Are you asking about this (example):

http://support.moosetechsoftware.com/solutions/txfspecs42.txt

And of course, you can start from csv, using tools such as:

http://easytxf.com/

Although this topic is dated, there is an Intuit VP responded here, and he makes one comment that the ProSeries implementation of txf isn't quite the same as for TurboTax:

https://personaleffects.blogspot.com/2009/03/turbotax-txf-specification-for-stock.html

However, it should be noted that txf is not Intuit's, but standard (open). Similar to ofx data being the financial institution standard.

I found this, too:

https://developer.aliyun.com/mirror/npm/package/txf-generator

Scroll at least half way down on this one, to bypass the changelog:

https://github.com/simonmichael/hledger/commit/da3ee26862ca41cf554cd59362c1d410ab107b22

And here's another sample file for reference:

https://www.dan.info/sampledata/download.txf