The floor plate release button pin is a solid pin.
Most any Model 98 Mauser version will fit or you can use a piece of drill rod.
Here's some places to buy one:
http://www.jackfirstgun.com/
http://www.poppertsgunparts.com/cgi-...a_gunparts.cgi
Part number M00225.
http://ssporters.com/parts/98%20Mauser.htm