This /dev directory is the exception from the rule, that everything would be a file. In this directory there are nodes,for the devices. Usually they are created on-the-fly by the kernel and its helper applications like hal.

The manual creation of /dev/mmcblk1p* device nodes with 'mknod'-command for the partitions of your external card, will not get you anywhere, because the underlying applications do not automatically start when detecting a node in that /dev directory, but rather vice versa the underlying applications do their magic and finally a device node is created in /dev,

There seems to be no way around the hardware detection around that infamous magnet.
Besides the magnet issue, you could check the contacts of the card reader for integrity (broken, malformed or worn down)

For software debugging you could try to give more information in giving the output of these X-Terminal commands. You need 'rootsh' package installed for these to work.