Sorry, I couldn't resist
Yes, John Claudino of Aztec makes them in N Scale. His website is
http://www.aztectrains.com/
The circuit i used is very simple, using a 3909 chip, a capacitor, and an led. the flash rate of the circuit was determined by the value of the capacitor. it would easily fit in an n scale boxcar & cost less than $3.00 to build. mine were
run off a single aa battery & power consumption was so low that a battery would power the circuit
continuously for about 18 months. the circuit was common in electronics circuit books at the time, i believe a version appears in the kalmbach book "practical electronics projects for model railroaders" by peter j. thorne.....
Tomar, the company that makes drumheads for passenger trains, also makes working EOT's (fka
FRED's) There are a number of deLuxe Innovations boxcars being auctioned on eBay right now with
working EOT's already installed if you are interested.