It also depends whether you are just after a recess for getting the mounting flange under flush to enable the clamping nut full engagement or are you looking for what is known as a cup wheel?
AXMINSTER POWER TOOLS list a 150×40 white alumina 80 grit as a spare for one of their grinders. From catalogue photos there is about 25 mm or so of flat rim. About £14
I think this is the company suggested by Michael Cox selling on Ebay.
This may be a suitable wheel for you. Cup wheel It does not say what grit the wheel is but you could ask them if it is suitable in other respects. I bought two cup wheels from them about two years ago and have had no problems with them.