I was looking through the reviews (added one to the 31mm Ltd - don't bother reading it, you know it's a great lens). Anyway I was looking at the reviews of the FA*300/4.5 and everyone says the same thing - no tripod collar.
I have the solution. It's from our good friends at Canon. I picked up the collar for one of their lenses that fits this lens barrel perfectly and the colour is a very close match to the Pentax lens body. Doesn't interfere in any way with lens function or operation.
I picked it up on (you guessed it!) Ebay for a very reasonable price:
http://cgi.ebay.com/Tripod-Collar-fo...dZp1638Q2em122
The added plus is that the logo is on the side that faces the body. So once mounted no one can see the Canon logo.