Silver-Etched Mace works great - if you are a macer. Otherwise you need to use a Runic Hammer to make one with Use Best Weapon Skill on it for a Fencer or Swordman.
You can also create one with a Runic Hammer. The odds are pretty high against making one, but if you burn a bunch of runics, you will eventually get one out of about 1,000 properties. 1,000 properties sounds like alot, but since a Bronze hammer makes weapons with 3 properties, each Bronze hammer makes (3 x 35 uses) 105, so 10 bronze hammers will make around 1,050 properties.
For the record, the way I determined you have 1 chance in 1,000 to get an Undead Slayer...
36 possible
Weapon Properties (2.8% chance of getting the slayer property)
24
Slayers including 5 possible super slayers. (4.2% chance of any specific slayer). I'm obviously assuming the chance of a Super is the same as a normal. From my experience, I believe it is.
So 4.3% of 2.8% = .1% or 1 out of 1,000. Be warned that these are only the odds of success. Your results will vary.