I don't think they were ever rubber.
My original 740 keys are hard black plastic by the feel of it.
https://www.ebay.com.au/itm/1X-VOLVO-KEY-BLANK-740-760-780-240-DL-GL-960-940-GLE-008-SPARE/142117154684?epid=869670928&hash=item2116d7af7c:g:~qcAAOSwyQtVzLRn
I ordered these 2 years back and they're just as good as OEM quality. Shipping was 2 weeks.