The Digi-Comp series mechanical toy computers of the 1960s became the introduction to computing for many a future geek. Here's the premier site on the Web to discuss these and similar fondly-remembered early "personal computers."
I remember getting an assortment of spring wire (from brookstone?) 30(?!) years ago advertised to last a lifetime. Perfect For smaller springs but running low
I found some 'music' wire at a local hobby shop which looks like it will be good for replacements. Three meters of the heavy gauge and 6 of the lighter one