I need to replace the chrome dash trim on my 70 cutlass S. Sadly the small trim piece that goes across the dash broke and fell off (long time ago) and I don't have the old piece. does anybody know where I can find or replace that part without having to do the whole dash?

 

any of the parts places like fusick or parts place will have that. I picked up a ~1/4" half round chrome bead w 3m adhesive strip at advanced auto and did mine its about the same size and fits in the channel nicely. it only cost about $10 instead of the $50 or so for the actual product idont think anyone can tell differnce except mine isnt falling off and discolored like the original was

 

The piece you're referring to is called 'Dash Bead Molding'. It comes with the small clips that bite into the dash to hold it in place. Most places have it for around 35.00 US. From Fusick catalogue:
Looks like this before install. Note the molding is preformed to match the corners and angles of the dowward side of the dash. Best time to install it is in the heat. Fits very well.