Last time I needed a guide bushing and couldn't find mine, I ca glued a piece of 3/4" OD PVC pipe go a piece of 1/8" ply. Double sided taped it to the base, plunged through and gave er hell. Just had to make sure the exact side was pointing toward the reference edge which was annoying but worked fine.
Out of my 3, there is one that I will always reach for first, it feels the best in hand and super easy to sharpen. Just put a mic to it and it measured at 28 thousanths. I'm sure it's the steel, not the thickness but you asked about thickness.