Do a google search on vintage and antique aquarium collectors. There's a bunch of collectors of all facets of aquarium history (tanks, decorations, filters,etc.)
The earliest Metaframes usually have a logo on the frame near one of the bottom corners but sometimes they don't. I have seen some of these smaller tanks on ebay for sale and people ask a ridiculous amount for them though they may not get what they ask for them!
As Oddball stated, a complete set up would garner a better price because the original lighting fixtures are almost always missing as are the stands.
Your tank looks very clean and the glass still looks great, at least with water in the tank. Many times the old glass gets etched and scratched and it tends to lower the price of the tank. I picked up a bunch of these SS framed tanks a couple years ago with the hopes of adding them to my fish room and some of them really need to have the glass replaced as it cannot be cleaned up. Sizes range from 2.5G to 55G and I paid about $1 per gallon for them. They are currently sitting in my garage waiting for me to decide which I will repair.
I hope you can get a good price for your tank, I love seeing these old retro aquariums still in use and in pristine condition.