First, if you are using meth regularly you are faced with two problems.
1. Meth causes vasoconstriction which narrows the veins to the point where they simply cannot be detected or hit. IV users know that more many people you cannot get a second shot in after the first one causes all your veins to shrink.
2. Meth will collapse or produce scarring that occludes every vein you use regularly. Especially if you use really concetrated/thick shots. Once this happens those veins will be practically impossible to hit ever again. It's confusing becuase you can still feel them but that is just the scarring/wall thickening caused by the meth as it goes through.
After 12 months of shooting meth 2-3 times a week (usually in binges lasting 2 days and trying to re-hit ever 4-6 hours) the veins in my elbows and wrists were totally gone. Even the doctor can't tap them when I need to give a blood sample.
For what it's worth, thisis one of the best IV harm reduction guides I've seen. It includes a section on finding veins:
https://harmreduction.org/issues/safer-drug-use/injection-safety-manual/safer-injection-basics/
One thing people do do is start tryng to hit deeper veins (like in the forearm) using bigger needles. I even had a friend buy a little electronic gadget that detected exactly where his deep veins were. But eventually, they'll just get as fucked as the ones closer to the surface and then you are really screwed because right now your body is using those deeper ones to work around all thecollapsed ones near the surface.