Hello gold131 and welcome to our 131 website and forum.
Being in the USA your best supplier for Fiat parts would be
International Auto Parts (
http://www.international-auto.com/) who I am sure will be able to help you.
In the UK
Demon Tweeks (
http://www.demon-tweeks.co.uk/) are an excellent supplier for such things as throttle linkages. Of course these days of the Internet and "click and buy" culture the location of the supplier is almost immaterial.
Please tell us more about your car and post some photos when you can. And of course let us know how you got on with the throttle linkage.