I have some that Dean gave me, it has not grown much in my system but I can give you some. Al least I can give you something for a change hopefully it will do better in your system how soon do you want it?
They both work but C. taxiflia is being banned as it is invasive, Caulerpa also gives off toxins which are not good for corals, etc. I think the effect of the toxins are over rated, it is highly invasive and should be kept out of your main display. It is extremely hardy and grows well when lit 24/7 to prevent sexual reproduction, increase carbon dioxide removal (stabilise pH) increase oxygen production and still removes nutrients.
Chaeto will perform the same functions when lit 24/7 but many recommend a more regular light cycle or reverse daylight.
I removed all my caulerpa at one stage and switched to chaeto, my chaeto grew well then crashed, only a tiny amount remained. I ran straight dsb for a while then introduced some caulerpa again and eventually both became established. I would get the chaeto and try that but if you want caulerpa I can give you some also. I'll be changing to chaeto only eventually.