Mechanical Resources:
- Surplus Parts:
These companies sell surplus parts (sometimes new, sometimes used,
sometimes refurbished). You can find very cheap parts here if you are
somewhat flexible in what you need and are willing to figure out how
things work (motors with encoders may come without data sheets, for
example, and you will have to experimentally figure out which pins on
the encoder are power, ground, etc...)
- New Parts:
There are many sources of various new mechanical parts, but
McMaster-Carr is one of the best, due to their excellent website, fast
shipping, and no minimum order. They don't carry many motors, but
carry all sorts of gears, shafts, linkages, bearings, and other
mechanical parts.
Electrical Resources:
- Surplus:
As above, many companies sell eclectic used electrical components and
systems. These are especially good places to get sensors and power
supplies.
- New:
- Information:
Many chip manufacturers have details and datasheets about their
components online. If you know the manufacturer of a chip, find
that company's website and poke around. Here are a couple places to
get started: