Ditto what Todd said. A clan chief posessing Arms really has no bearing on the existence (or availability of) a tartan. For instance, Spalding has had Arms forever, but you'll find no Spalding tartan. On the other hand, you'll find plenty of tartans that have been designed for non-armigerous families.

In any case, the two things are different, so it's like comparing apples to oranges.

But I wanted to write about the MacTavish tartan being "rare." Not the one in your picture. Just about every woolen mill does this one, sometimes in a variety of weights. For instance, Ingles Buchan does it in a tie weight. Lochcarron does it in a 10 oz and a 16 oz fabric. It is actually pretty easy to find, as far as tartans go.

One thing to keep in mind is that "MacTavish" and "Thompson" can be used interchangably to refer to the same tartan. So if you don't see it listed under one name, look under the other. There is a red version of the tartan, a blue version, a brown, a grey, etc. Usually the red version is sold under the name "MacTavish" and the others are sold under the name 'Thompson", but this is not universally true.

House of Edgar, in their 13 oz cloth, does produce a variation of the MacTavish from 1850 as part of their "old and rare" line, and as far as I know are the only mill producing it. So maybe this is the one you mention? It is quite different from the usual one (seen in your picture).

On another note, about your sporran, I really like how the portion of the tartan used in the flap corresponds to the portion that would be behind the sporran on the kilt (only on the bias). I like it! I don't think it would have looked as good, however, if a different part of the tartan was used. Was this intentionally done, or just a happy coincidence?

Aye,
Matt