I did not have any trouble finding m600 lens boards in 25 mm and 39 mm of ebay. First decide on which lens mount size you're going to use and then buy your board. I suggest you buy a separate lens and board for the two formats. The boards switch out very quickly and with good glass going cheap, it should not prove too difficult on the wallet.
I mostly use the glass carrier that comes with the enlarger, but a simple glass-less carrier can be made of two pieces of medium or heavy-weight black mat-board hinged together with black(ened) paper tape. Take your time and do it right, clean with square cuts, and don't forget to use a Sharpie to black out the cut edges of the windows. More than one professional photographer has taken the path and it's great because you can have both a cropped and full frame carrier for 35 mm for little brass.
Also, don't forget that these enlargers can do smaller film sizes, so if you're like me and have a Minolta 16 that you're dying to put back into action, keep an eye out for a 25 mm lens and cut those carriers smartly!
Did you get a manual for your enlarger? Here is a pdf of it for download;
http://www.darkroompro.com/pdf/enlargers/durst_m600.pdf
Pay attention to the section on centering the bulb correctly for even illumination.
Cheers