I suppose it is still available at KDH, but stock is running out quickly.
Check here:
http://www.kdh-amiga-shop.com/catalog/default.php?manufacturers_id=17I'm not sure where you're from, so you could contact E3B about who's selling these cards at which countries...
I used to have an X-Surf I board for a few years, it worked okay (together with a HyperCom module), but I've exchanged it in favour to the above combo (the X-Surf-HyperCom sandwich was tricky to mount because it actually took three slots height on the ISA/video-slot side). No need for the HyperCom anymore as I can now connect my printer via USB (much faster) and don't have use for the serial ports anyway (thought there are also USB->serial adapters). And as I don't have any IDE-devices in my A4000T, the extra IDE ports on the X-Surf were used only on rare occasions when replacing a hd and copying from on disk to the other). And Norway is just sooooo tiny

However, it really depends on your needs.