Free Railroad spikes on CL in Dallas:
https://dallas.craigslist.org/dal/zip/5314931599.html
“Very old railroad spikes and other track assembly. About 100. Come get them near downtown Dallas. Contact Sharon at xxx-xxx-xxxx”
Looks like they weigh about a pound a piece (or a bit less).
Seems like they might be good for blacksmithing, based on my complete lack of experience, or maybe some other fun project surrounding railroad paraphernalia…