Just go along the tracks when they replace ties they usually use new spikes and just throw the old ones on th ground around them just look around for them.
P.S. look for ones that have HC stamped on top those mean high carbon they only have like .3% carbon( if i am wrong just correct me) but when put in an ice cold water quench or super quench it hold a fair enough edge. the ones with a $ stamped on top if i remeber correctly are a copper ,steel alloy but im not positive. Staff addition: WARNING do NOT take or STEAL anything from the RR tracks, This is a Federal offense and there are many discussions on this Illegal activity in the forums