128MB Black Diamond Memory Module for IBM ThinkPad T Series T21 (Type 2647) SDRAM SO-DIMM 144pin PC100 100MHz Upgrade System Specific Memory - Newegg.com
IBM Thinkpad T21 - BMSoftware laptops
IBM THINKPAD R51 R52 T20 T21 T22 T23 T30 T40 Port Replicator Docking Station $41.69 - PicClick AU
256MB Memory for IBM ThinkPad T21 2647-4AU PC100 SDRAM 144 pin SO-DIMM Laptop Notebook RAM (PARTS-QUICK Brand) at Amazon.com
Was excited to get my t21 today from ebay - got this sticky, badly corroded r31 instead. Probably one of the worst condition thinkpads I've ever seen... : r/thinkpad