I found a good site on arthurian heraldry. Perhaps it has been posted before, I could not find it.
http://www.theheraldrysociety.com/articles/fictional_attributed/arthurian_arms.htm
(the scrolling page is making me insane though)

An interesting note:
King Lot's shield is Purpure, a two-headed eagle displayed or, beaked and membered azure (Gawaine's shield). Instead of the traditional "lot" heraldry, Argent a Canton Gules. I'm not sure about the accuracy of this though.

Interesting
Much the same as the sources I used
Be sure to see http://gspendragon.com/lesarmes.pdf, contributed by a French friend of mine
Alas, we have not gotten the pictures for it


I found a good site on arthurian heraldry. Perhaps it has been posted before, I could not find it.
http://www.theheraldrysociety.com/articles/fictional_attributed/arthurian_arms.htm
(the scrolling page is making me insane though)
An interesting note:
King Lot's shield is Purpure, a two-headed eagle displayed or, beaked and membered azure (Gawaine's shield). Instead of the traditional "lot" heraldry, Argent a Canton Gules. I'm not sure about the accuracy of this though.

Accuracy is almost not relevant here, since they are all fantasy characters
Also, in the earth phases of KAP the kings are likely to use several coats of arms
That having been said,
the two-headed eagle is given to Gawaine by none other than the Pope, at whose court he was raised, in a splendid little story written in Latin called The Knight of the Surcoat.
Now, I don't include that tale as part of the canon for KAP
and I include it here only to point out that the origin of these arms was that story, and that they were given to Gawaine.
Hence it is is unlikely that his father would have had them.
OTOH, maybe Lot DID have them and hence handed them down to his son(s)

...the two-headed eagle is given to Gawaine by none other than the Pope, at whose court he was raised, in a splendid little story written in Latin called The Knight of the Surcoat.
Now, I don't include that tale as part of the canon for KAP
and I include it here only to point out that the origin of these arms was that story, and that they were given to Gawaine.

I like that tale! If you WOULD place it in your KAP-canon, what year would this take place?

...the two-headed eagle is given to Gawaine by none other than the Pope, at whose court he was raised, in a splendid little story written in Latin called The Knight of the Surcoat.
Now, I don't include that tale as part of the canon for KAP
and I include it here only to point out that the origin of these arms was that story, and that they were given to Gawaine.
I like that tale! If you WOULD place it in your KAP-canon, what year would this take place?

I really don't know
It would require quite a few changes to make it fit
Let us know what you decide!