I have researched a few possibilities and found a few companies that do actually manufacture custom dipsticks.
For the tube, however, if I was unable to find one in a junkyard or eBay, I would fabricate one from thin wall steel tubing. Match the dipstick hole diameter in the block and possibly weld a larger diameter tube that accommodates the factory dipstick itself to the smaller diameter dipstick hole tube. To make things easier, I would probably just bend up tube that is one diameter only, the diameter of the dipstick hole in the block. I would then fab a dipstick using some stainless steel cable with a crimped on level indicator. Fabricating the handle would need to be done using some roundstock. Drill a hole through the body of the handle's primary axis to accommodate the cable end, then drill a lateral hole halfway through the handle to then tap it for the thread matching a set screw and retain the cable to the handle in that manner.