Had been looking around for some, and while it is available I thought I'd have a go at making it myself, which turned out to be a little more expensive, but not as rewarding as DIY!
So, I found a thread on CFTF - 7 parts rosin (I used a small block of violin rosin I got on ebay for about $5), 2 parts beeswax (ebay ~$5 for 3 blocks - enough for about 100 years supply of cobblers wax) and 1 part oil - olive, castor or tallow)
More rosin makes it more sticky, more beewax makes it softer but less sticky - mine came out just how I wanted it.
As I didn't have a digital scale, I used the very scientific method of eyeballing - trust me, I'm a biochemist!
I put the rosin and beeswax in separate freezer bags and hit them with a hammer to break them up. The rosin I hammered until it was a powder, didn't take long.
Next, I put the powder in a new cheap sauce pan (the most expensive part at $7.50 from the dollar store - go figure - $7.50!!) with a dash of oil, again eyeballed, and a piece of beeswax I guessed to be about the correct size and put it on max heat! I bought a new pan as the 'boss' wouldn't let me use the cooking pans. I stirred it with a 'wife approved' spoon from the drawer, it took about 5 mins for everything to blend together to a nice runny liquid.
With a lack of silicon cup cake shells, I just used a freezer bag to pour the liquid in and once it was cooled a bit I put it in the fridge with the edge under a milk bottle, allowing the bag to hang at an angle that the wax would solidify in the corner.
Half an hour later I had this....
A nice tacky piece of wax that should be great for heads on salmon flies, and would probably work well for dubbing bodies too. Sticky as all hell, and a bit of a nightmare to get out of the bag - I'll definitely use the silicone cup cake shells in future as a mold rather than the freezer bag method. There was very little residue left in the pan, so I'll keep it for future use.
The other alternative was to buy some cobblers wax for about $10 for 4 small pieces - 2 light and 2 dark - plus shipping, but where's the fun in that, huh????