Premium Bandai puts up listings for Kamen Rider Zi-O and similar merchandise on their English site.
On their English speaking site, Premium Bandai has carried over several of their Kamen Rider Zi-O costume pieces, along with general Kamen Rider Zi-O brand clothing and the recently revealed Live Action Watches. Some of their new content also includes other Japanese series, such as Ossan’s Love.
Previously, Premium Bandai was an online shop exclusive to Japanese residence, but within the last few years has expanded its reach to the overseas market.
Source: Premium Bandai US