Available four chars domains with results in the WayBack Machine

As always all of them were available at time of posting.

kfmn.net
stk9.com
ukef.net
wjcr.net
5dkj.com
20rb.com
w1bt.com
gnmz.net
4sud.com
7rwf.net
m2mv.net
hzzs.org
ycld.org
3xzq.com
cnh7.com
bcaj.org
izaq.net
jb15.com