So you need a 1.5 mm spacer for the right side, assuming the axle was properly set up for the old freewheel. (Actually what you need is 3 mm of clearance between the outer face of the smallest cog and the face of the locknut. Use that as your benchmark.) Then don't forget to remove 1.5 mm worth of spacers from the left side to keep your OLD at 126 mm. Even if your OLD has to increase to 127 or so (because sometimes you don't have enough spacers of the right combination of sizes to make it come out exactly right), that will still give you 3.5 mm of axle sticking out beyond the end of each locknut. This is loads -- more than enough. You will need to re-centre the rim.

If you really feel you need 5 mm of axle at each end, buy the 141 mm and cut it down to 136 or 137. I've done this with really long axles to build tandem wheels, which need 145 mm OLD, out of single-bike hubs -- it works fine.