For the ex era it’s indeed a bit more difficult, but from what I’ve personally seen the distribution seems to be roughly equal (maybe 30-70 or 70-30 for some sets). I never had any trouble finding certain ex era sets in both 1st and unlimited edition personally.
And as mentioned by @pichufan , the World Champions Pack - which contains cards of the English EX Power Keepers set - was released after the EX era.
I’ve also posted this a few months back for 1st vs unlimited edition Japanese releases across all eras for those interested: www.elitefourum.com/t/is-unlimited-more-rare-than-1st-ed-in-japanese/27621/4
Greetz,
Quuador