Hello.

I have built a few of these over the years.
Reference sources, a precise standard known value.
I normally build a device that provides a precise frequency output as well as a precise voltage source.
For frequency you may want to consider something like this.
http://www.goldmine-elec-products.co...?number=G13110
For voltage, this or something like it.
http://datasheets.maxim-ic.com/en/ds/MAX6143.pdf
I use a weatherproof electrical "handy box" as this is a cheap very rugged metal or plastic box.
For powering the box proper I use a wall-wart, whatever is cheap at the time.
To power the TCXO I use an LM 7805 that is rated at 2 to 3 amps, cheap.
The whole thing if bought new might run you $20 not including shipping.
And there is no reason you can not have several TCXO units on a selector switch.
In my case I have several CATV amp IC chips and so both buffer and bring the level of the signal up but this is not essential by any means.
And there is no reason that this needs to be in another enclosure, you can build it into your radio and have it as a "spotting" source, but with some real precision behind it.
You can use your imagination and come up with something altogether new.