You might have some luck searching vendors for industrial/military/aerospace applications of SD memory cards. I noticed Panasonic has product available starting at 512MB, but not sure of prices.
Here's a link to
ATP. They too start at 512MB at around $20 CAD and around $30 CAD for 1GB. Not cheap, for low capacity SD cards, but I suspect you might not have a lot of luck in the general consumer market finding the original 2GB or smaller SD cards (as opposed to SDHC or SDXC). You can also order these through
MyDigitalDiscount. MDD also lists the
Ridata 2GB SD card for $7 US but requires a two-week lead time.
From
Wikipedia (note - they refer to the original SD cards as SDSC):
All SD cards let the host device determine how much information the card can hold, and the specification of each SD family gives the host device a guarantee of the maximum capacity a compliant card reports.
By the time the version 2.0 (SDHC) specification was completed in June 2006,
vendors had already devised 2 GB and 4 GB SD cards, either as specified in Version 1.01, or by creatively reading Version 1.00.
The resulting cards do not work correctly in some host devices.
SDSC cards above 1 GB:
A host device can ask any inserted SD card for its 128-bit identification string (the Card-Specific Data or CSD). In standard-capacity cards (SDSC), 12 bits identify the number of memory clusters (ranging from 1 to 4,096) and 3 bits identify the number of blocks per cluster (which decode to 4, 8, 16, 32, 64, 128, 256, or 512 blocks per cluster). The host device multiplies these figures (as shown in the following section) with the number of bytes per block to determine the card's capacity in bytes.
SD version 1.00 assumed 512bytes per block. This permitted SDSC cards up to 4,096 × 512 × 512 = 1 GB,
for which there are no known incompatibilities.
Version 1.01 let an SDSC card use a 4-bit field to indicate 1,024 or 2,048 bytes per block instead. Doing so enabled cards with 2 GB and 4 GB capacity, such as the Transcend 4 GB SD card and the Memorette 4GB SD card.
Early SDSC host devices that assume 512-byte blocks therefore do not fully support the insertion of 2 GB or 4 GB cards. In some cases, the host device can read data that happens to reside in the first 1 GB of the card. If the assumption is made in the driver software, success may be version-dependent. In addition, any host device might not support a 4 GB SDSC card, since the specification lets it assume that 2 GB is the maximum for these cards.
Bottom line from reading the above is with a 1GB or smaller SD card, you should be OK. It's with 2 and 4GB SD cards that you may run into problems, depending on what SD protocol version the Epson R-D1 uses (and there are different versions of the R-D1, which each might differ - the X version is SDHC compatible and looks like the S version is just a firmware update of the original).