I went on NicoNico and searched up "MEIKO_ENGLISH", there's surprisingly plenty of content. It is all old videos, but it's a lot more than what you can find on YouTube.
Didn't have much luck with searching "Luka English" though.
I want to discover more work featuring classic English voice DBs. I don't mind covers, I just want to listen to the unique machine noise of a pre-AI Vocaloid.
I must say though, AI voicebanks handle bass sound and lower notes much better.
edit: I also recommend to send them as attachment a PDF document with the detailed description of the figure, artwork, images and reference links of artist pixiv / piapro / niconico (●'◡'●)