Rare coralline algae scrapings?

I've been looking into seeding my tank with scrapings as opposed to introducing live rock, as it seems to be a cheaper alternative. I'm curious though.. Most tanks I see have a lot of purple corraline algae. Is there a place, or a person, I could buy some different colored algae scrapings from? I see a lot of turquoise algae, yellow, red, orange, etc., online, but can't seem to find where to purchase seeding rocks or scrapings from. How do I get those colors, as opposed to the (seemingly) common purple? Are there specific tank conditions that encourage the colors im looking for? I can't seem to find the answer online. Thanks in advance!!