The most common source for purchasing a SCR-625 mine detector is ebay. Do a search on 'mine detector', and also try mine sweeper, or mine.
Caveat Emptor - let the buyer beware. It is easy to hide defects or even disguise that parts are missing by poor pictures, and just a general lack of disclosure. Too often the sellers take pictures of ID plates and almost ignore the detector itself. Few sellers are conscientious enough to point out obvious defects, much less smaller ones. Watch for cable issues, and beware of the seller that doesn't take the detector out of the box, or open the amplifier. Look carefully at the cables, where the cables come out of the control box and amplifier box. This is the most likely place for a cable to be bad. Some who are not familiar with the SCR-625 may not be aware of what is missing, but should be able to give some indication of defects. Most that I have purchased have had some issues; one even had the control box to search coil cable replaced by three lamp cord wires. This was not visible in the pictures, nor was it disclosed. Probably one in four has a serious issue that is not disclosed. Another ploy is to say that it "probably" works, because it looks good. From various ebay ads: "Not guaranteeing it works, but I bet it could be made to without to much effort." ,"There is a very good chance that this machine is in ready working order","I was told that it works but do not have any way to test it" and "It is complete. I bet with some new tubes and battery this thing would work, cant say for sure of course." " I'm not sure how to use this piece so I can't really check if it works... but I don't see why not unless some wires got to old and weak?", "...with instructions and spares, probably fully functional.", "Styles may vary from the one pictured. " (so what ARE you getting here?), This item is new old stock and has never been used. (this was description on a scuffed up M356 speaker)
Questions to ask:
Is there any corrosion?
What condition are the cables and connectors in?
Are there any apparent problems?
Do knobs and switches move smoothly?
Caution when buying a detector! A number detectors I have seen and heard of, are missing the third piece of the handle! Be sure it has the piece farthest from the search coil if buying one! This is easy to overlook when buying a detector. Oct 2013 - A model H detector on ebay with two sections of handle missing. No mention of it in the ad.
Many ebay sellers say nothing about condition, so if you don't ask, it's hard to file a negative report if you get a pile of junk. I am more inclined to buy items from a person that lists some defects, rather than one that says it is in good condition, or says nothing about the condition.
An interesting exercise - search for "rare" on ebay - a recent search in all categories found over 1,200,000 "rare" items for sale.
As a technician with over 30 year’s electronics experience, I know that you cannot tell that something works by looking at it. If the mine detector has not been repaired in the last 40 years, it will not work. Would you expect to just drive off in a car that has not run in 10 years? Of the fourteen detectors I have worked on, the best I have seen without repair was just a feeble tone with a large metal object three inches from the search coil.. Lastly, most sellers will say it is complete, when it is missing many accessories. I have never seen a complete detector anywhere. Just look for the basic stuff, at least.