Filling Higher Value Ctos

My collection, like most everyone, is lacking set completion (blank spaces on a page ) on the very common, mostly CTO sets. No problem filling the classics but the modern blank spaces need some addressing as well. What is the best means of filling these spaces? The largest percentage are extremely low catalog value. Are the SCF dealers interested in want lists on these? If yes what should I expect to pay as a percentage of catalog value. Does one take a want list to a show?(I will be attending the SE Stamp show in January). Most of what I am looking for is up to 1975 but some go as far as mid 80's. Approximately 40 countries that will be starting the beginning of next year.

For some "tough to find" used, modern stamps, I buy first day covers and soak the stamps. This is after I figure out that it may take me a long time to find a stamp...if I ever could find it at all. First day cancels are presentable alternatives until I can (hopefully) find postally used copies. In some cases, they are not immediately recognizable as first day cancels. Generally, they are somewhat cheaper than postally used stamps.

As a last resort, I sometimes buy a c.t.o., but only if a stamp is really elusive, and it is very, very cheap.

I make pencil notations for first day and c.t.o. cancels in my albums, as a reminder to upgrade.

Looks like the best way to do this is purchase mint year sets. They are somewhat reasonable and won't have the ugly CTO cancellations.