Finding US singles is hit or miss in Japan. You could find just the card you're looking for - I've found a few cards from the 1990s on that I needed for sets and player collections. Or, completely shut out - I can find packs of 2018 Topps but I doubt I'll find singles, and only a handful have found their way onto Yahoo! Japan Auctions.
And then, many of them are overpriced. Are you willing to pay $3 for a Jose Altuve base card from 2018 Topps? Neither am I. But there are plenty of hidden gems, like the cards in this post; all of them came to me for 100 yen ($1) each, plus about 100 yen shipping total.