"How can you have foreign "floorsweepers"? Were their chips made in the USA?"

Many were and are still made in the US.

"Are there actually any really
rare "floorsweepers"?

IMO, NO.

"Can "floorsweepers" still be found at the current manufacturers?"

Of course but now there are strict gaming regulations and internal company policies concerning them.

"If you have "floorsweepers" from a defunct manufacturer are they "RARER"?"

IMO, No. Most collectors now realize what they are.

When the old manfacturers like the Mason Co, TKS, Taylor Co, Hunt, PCC, etc records were bought up by collectors, 100's of these things were included in the purchases. Also many sample chips that were never produced. There was also floor sweepings of the ones never produced. I have Moose lodge chips from Moose lodges with numbers 2000 above any Moose lodge that ever existed. Also Eagles Aerie lodges with the exact same high number.

I also love them and buy any I see at reasonable prices.
Some dealers try to sell them as error chips. They are not errors.