I have ordered plants from YourFishStuff on Ebay or their website, AquariumPlantCenter on Etsy, and rolandpre6 on Ebay. All three have huge variety and decent prices and deals. If were me, I would look to add some variety and color to the tank. I would get red ludwigia and a tiger lotus to bring in some red and interesting shapes, as well as balance the tank a little bit with those large leaves the tiger lotus has. Maybe an anubias barteri. The dark green and broad leaf shape would really pop by the anacharis, more so if you had some red ludwigia too. Maybe a couple amazon swords in the back. I have found swords to be really great space fillers! They create a really nice "backdrop" for darker plants or red plants or very defined plants without looking "solid" like a background.
Edit: I have been the most pleased with YourFishStuff. 1 anubias barteri really has 2 individual plants, 1 amazon sword really comes with 3. The red ludwigia from them came with like 8 12" stems! So in your tank you could get by ordering 2 swords, 1 anubias, and 1 ludwigia
Edit: I have been the most pleased with YourFishStuff. 1 anubias barteri really has 2 individual plants, 1 amazon sword really comes with 3. The red ludwigia from them came with like 8 12" stems! So in your tank you could get by ordering 2 swords, 1 anubias, and 1 ludwigia