Ahhh, yay,
(if the links don't work, email me if you want them)
I just had a look on internet hobbies. Nothing came up, so if there is a kit, it might be an out of production one.
Well, you are right about the conversion tho. It is done by Red Roo Models and is in 1/48 scale.
http://204.50.25.179/features00/avonsabrepm_1.htm - this is a website that shows how one modeler did it, it might be of some use to you.
Also the Red Roo Modeling companies web site is
http://www.redroomodels.com/ - i believe they send overseas if your keen on getting the conversion.
Laters