Bob Roberts sells them.
http://www.therealbobroberts.net/parts.html#hardwareAnd the details:
Carriage bolts 8-32 x 1/2" shiny w nuts (Pac CP) 10 for $3.25
Carriage bolts 8-32 x 1 1/8" yellow 4 for $2.00
Carriage Bolts 8-32 x 1 1/2" Shiny 10 For $4.00
Carriage Bolts 8-32 x 1 1/2" Black 10 For $5.00
Carriage bolts 3/16" x 1 1/4" black 10 for $2.00
Carriage bolts 3/16" x 1 1/4" stainless 8 for $3.00
3/16" x 1 1/4" Black Carriage Bolts 10 For $4.00
Carriage bolts 3/16" x 2" black 10 for $2.50
Carriage bolts 3/16" x 3" black 10 for $3.00