Sunshine still has mini-kits for the square corner versions.
At least, they had some at Naperville last fall.

Tim O'Connor

The IM model can reasonably
accurately represent nearly all cars listed in the roster. Cars built
for Erie and EJ&E are considered exceptions and cannot accurately be
modeled using the IM kit without making major changes.

Brian,
Sorry for the extra bandwidth, but after sending my reply I realized
that the IM model (having ends with round corners) cannot be used to
accurately represent prototype cars with square-corner 5/5 Dreadnaught
Ends. Thus, I revise my statement by limiting it to nearly all cars
listed in the roster having round-corner ends, which excludes cars for
Soo Line, DSS&A, and some IC cars.
Regards,
Ed Hawkins