Im not sure what they go for, but I've seen some advertised in the mechanical for sale section. Most people call them the speedometer gear for the trans.
Tony (Whitepunkonitro) has a good stock of parts and sells them at reasonable prices, plus he's a good guy to deal with. I have dealt with him a few times and just got some parts from him yesterday that we ordered a week and a half ago. :cheers:
You need to know how many teeth that you need so the spedometer is calibrated right. They make them in different teeth for various tire/gear ratio combos.
FYI:
http://www.forabodiesonly.com/mopar/showthread.php?t=222219&highlight=trans+speedo+gear
http://www.forabodiesonly.com/mopar/showthread.php?t=231318&highlight=trans+speedo+gear
http://www.forabodiesonly.com/mopar/showthread.php?t=235973&highlight=trans+speedo+gear
http://www.forabodiesonly.com/mopar/showthread.php?t=300307&highlight=trans+speedo+gear