There is currently only one manufacturer of Poly/Viscous Tartan fabric. That is Marton Mills.
Believe me, if there were others Rocky, Pete or I would know about it. That's our job.
The fabric from Marton Mills weighs 375 grams per linear meter or 9.75 oz /yard.
The fabrics that are advertised as heavy weight P/V are usually 100% Polyester or Acrylic. And the term heavy weight is very subjective. Fabric is normally listed in weight for a piece 60" wide by 1 yard long but some manufacturers use a different system.
I know of only one length of true 13 oz P/V that has ever been woven and that was a test run done by Fraser & Kirkbright in Vancouver of Black Watch Tartan. I had a 4 yard piece of it and weighed it and it was exactly 13.1 0z.

As a side, I also weighed some of the fabric in kilts that are coming from mills in Pakistan, India, and China and they weighed out at 4-5 oz even though they were listed as 13 oz.

I'm not knocking those fabrics but the truth right now is that our world of Tartan is so small that it just isin't cost effective for mills to produce. So we are in a cunundrum. Accept light weight Acrylic fabrics or raise such a stink that the mills start to produce what we are asking for.

Bottom line, be suspicious of claims of heavy weight P/V Tartan fabric that is listed as P/V until proven to be so.
Do a search here for the burn test that you can do to determine what composition your fabric is made from.