Very few product areas where NiCd are allowed to be sold within EU. And I think some of these areas will be reviewed this year, so they will probably be forbidden (if it hasn't happened already) for power tools too.

Most probably, these restrictions will spread outside EU too, making it impossible to find spare part replacements.

One issue to consider here is the number of cycles you need. Most battery technologies are managing way less than 1000 recharge cycles so unless you have so big batteries that they can handle multiple discharge bursts within the same discharge cycle, you may not be able to find any acceptable battery technology.