For the tail lights, and if you want the real McCoy, used will be your only option. Along with finding good lenses, one must assess the condition of the reflector and chrome bezel (since they are all attached together). It appears from other postings that the relector can be removed (with care) and replaced or plastic plated. I believe Eastwood sells chrome spray paint that is supposed to be the most reflective paint one can buy.
There is also the option of reproductions (which are available through Millers and Buds Benz). To switch from original lenses to reproduction will require the purchase of red repro lenses, reflectors and bezels. This will total $900 for the pair.
While either road is expensive, at least now there is the availability of quality red reproduction lenses!
In regards to the parking/fog light lens bezel combination (USA), all three styles covering 1963 through 1971 are available for around $300 each.
Best Regards,
J. P. Mose
1968 250SL