If you had to? They're easily found. I just get mine where I get everything else, at Newegg. Only $50.
Yup. The WRT54GL aka WRT54G v4 is still a current Linksys product.
It seems to me that the culture at Linksys/Cisco won't breed another model like the WRT54G/L
The newer routers just aren't as popular for hacking as the WRT54G. They've also not done a significant hardware/software change due to cost reduction like the WRT54G so a WRT54GL style model isn't necessary.
The Linksys products aren't actually designed by Linksys/Cisco. The hardware designs and software are all purchased from design companies. I can't remember who actually designed the original WRT54G but the source code has their name plastered all over the place.
I've replaced all of my WRT54Gs now with Cisco APs.
I have an intense dislike for DD-WRT, as they don't have the first clue how to make the process user friendly.
I've found DD-WRT to be similar in operation to the stock Linksys firmware. If you can configure the stock firmware then you can configure DD-WRT.
Go look at OpenWRT if you want "non user friendly" :P