http://cgi.ebay.com/Toshiba-1-8-30GB-HDD-MK3006GAL-CF-PATA-5MM-Hard-Drive_W0QQitemZ250490815805QQcmdZViewItemQQptZPCC_Drives_Storage_Internal?hash=item3a526a853d&_trksid=p3286.c0.m14The above link is an eBay auction where you could have purchased the 1.8" drive. They may not have 160GB drives in that size, but you can definitely get a drive larger than 4 or 8GB.
The best thing to do is go to eBay.com and watch for the best deals on 1.8" drives. Pick the one you think is best and make sure the seller has a good rating.
There may be other locations online to purchase them, but you would have to use Google to find them and eBay would be my first choice.