I've read that large hostas can take up to 7 years to reach mature size. If you're buying plugs, I'd suggest buying 3 and pot them all together for a couple of years. I always pot my liners until they get some decent roots.
Anyone on Facebook? There's a group called Mike Giese's Hosta Stop seedling for sale
I bought 2 from him last year. Here's what I'm getting from him this year
