The DR-DOS/OpenDOS Enhancement Project

The NorthTec's Gecko Edubook can be interesting for you. It doesn't feature pcmcia but is a new hardare that is quite low power and able to use AA or lithium batteries. It lasts 4 hour under AA batteries, 6 hours under Lithium ones.

Not sure about DR-DOS compatibility, but it uses a chinese x86. It's DOS compatible and the manufacturer provides tools for DOS, including ethernet drivers and more.

DOS

* DOS NDIS Driver
* Novell Netware Login Script
* Ethernet Packet Driver
* DMP DOS SPI flash disk tool, for external SPI Flash.
* DMP DOS Socket Library
* DMP Serial Port Library

The Xcore chips are able to change speed under DOS or Linux too, maybe that can improve the compatibility with old software:

I don't know of a product similar to what you want. Maybe some netbooks (but they lack pcmcia too), but I suspect they can have some compatibility problems with DOS.

There are adapters to connect pcmcia cards to usb like the the adapter from Elan Digial Systems, but not sure if those work under DOS.

If you don't mind getting a second hand one, there are tons of options out there. But those laptops can be quite used, so beware of getting an extremely good model (robust design, excellent manufacturing... there are few like that).