dried bashed nettle stalks work alright for short order wicks.
The earliest aussie slush lamps I can find an aussie ref. For were cut down kero tins, filled with mutton fat and used floating chunks of dry cow manure as a wick.
Rushlights UK style weee Junca spp. reeds, peeled and weathered and dipped in pig lard, rarely mutton fat. A source I have lists 6 to 1 lard to rushes, and a burn time of about 70mins for a full rush.
In ost other countries bulrush means Scirpus spp. Here usually Typha.
I save old veggie oil for lighting in blackouts, use double or triple twined jute garden string for wicks, and my favourite for lamp bases is salsa jars - low, stable, sturdy, and excellent lighting for tabletops. I make reflectors out of coffee cans if needed and wick holders are wound out of coathangers or folded from steel taken from coffee cans.
Makes the place smell like a cheap takeaway but very useful. I always use an oil water mix, seems to prevent overheating and you can burn the last drop of oil.