I needed leaded solder recently too for a vintage audio project, I'm in the UK and while it was a bit of a faff to track it down initially I was able to order some locally. Might get better shipping buying from the UK next time!
It's not like it's banned or anything, it's just not allowed to be used in (most) consumer electronics.
"It is restricted to professional users and cannot be supplied to the general public (non-trade customers)"
Are RS Online gold-plating the regulations? Probably. I bought from Digikey USA instead.