NiCd batteries indeed do have the memory effect and this cannot be recovered. So after a few years they need to be replaced.
I'm in the same situation but with a Bearcat scanner. When I tried to get replacement batteries the shop told me that the sale of NiCd batteries is no longer allowed due to EU regulations. They're not exactly environmentally friendly when disposed of. And of course NiMh or LiIon batteries are not supported with a NiCd charger.
In the end, I'm not using that scanner often enough to invest any more time. I have both a 220V mains and a 12V car adapter and that covers my needs.
In your case, I would contact Icom directly and see what they have on offer. Then hit eBay to see if you can get the same product cheaper somewhere else.
in any case, don't buy 2nd hand NiCd batteries. You may be disappointed.