Origin Of Bulk Non-Us Coin Lots On Ebay?

The answer to your question is, "Yes".

While some US dealers refuse to handle non-US coins at all, many have a bucketful of common world coins they acquire, mainly through returning tourists and estates / collections acquired. Many of these dealers don't really sell too many of these foreign coins themselves, so they just accumulate in the shop. When the bucket gets too full, they offload them in bulk, either to a wholesaler or regular contact they have, or on ebay.

There are also large bulk coin processors. One of the most famous are the central banks in Germany, which bag up and sell all the foreign and obsolete coins handed in to the banks in that country. These "Bundesbank bags" are an excellent source for bulk coins. I think the standard Bundesbank bag is 10 kilograms (22 pounds). I bought one last year; see this thread for a breakdown of it's contents.

Bundesbank bags and similar "unsearched" lots are likely to contain more interesting things than a "searched" pile that came from a dealer's scratchtray.

I have a small jug of non-US coins that I pick up on my trips outside the country, thanks to the government. Most military finance offices don't (won't) exchange coins (paper only) when you leave the country.

Who knows, these may go up for auction (sorted by country) when I get tired of them. My girls like to pour them out on occasion and locate the countries on the map...so they are fun and educational!