I did do a search for carriage stops and did not find anything like the one I have just modified that I use.
The original one that I made quite a few years ago was a simple block of brass with a 5/16 rod and a couple of 1/4 x 20 allen head cap screws to lock it.
On another forum a chap had made one almost identical to the one I made and mentioned that he also had a set of slips to go with it.
It occurred to me that it would be possible to modify my simple stop to be able to easily make it have multi positions.
The first step was to add a couple of brass sliding stops to the 5/16 bar which gives two positions.
then remembering the comment about the slips I added a holder at the carriage end to take one of the 6 x 1/4 inch diameter slips that are set to 1/4 inch increments. so with the two positions at the block and 6 different slip lengths I can get 12 repeatable carriage stop positions.
The last thing was to replace the allen head locking screw (the allen key often fell out) with a locking lever type screw.