HI Jude,
I don't have any plants at moment so can't help you.
I used to have a small amount of Echinodorus tenellus. Don't see it in the shops at all.
You may be able to find Lilaeopsis novae-zelandiae, after all it is a NZ native. It could, under the right conditions, be a subsitute.
Often tenellus turns out to be an underdeveloped version of Echinodorus quadricostatus also called the 'chain sword'.
Don't know about the other plant