In fact, many of the various former and current Thomas VAs in Japan did voices for Anpanman characters!
Keep Circulating the Tapes: With the series being as long in rarely exported, year-sorted episode packs in VHS and DVD with about a dozen each year, many, many episodes have never been officially released for home viewing. Likewise, with a publication history spanning the better part of four decades and 100+ titles, a large number of older Anpanman books are out of print (the 25-volume "Anpanman Mini-Books" series from 1983-'84 was only recently republished), and some stories (including the entirety of the monthly manga) appears never to have made it out of the periodicals where they were serialized. The last three years' worth of the newspaper strip (whose books only cover the first 18 months or so) is relatively easier to obtain, provided you have access to a library that collects old issues of the Yomiuri Shimbun....
No Export for You: Despite its popularity, the Japanese food-centric characters make it something of a hard sell in the Anglosphere.
Recycled Script: Happens from time to time, given the length of the series and its adherence to Strictly Formula. It also affects the movies, which are generally based on existing books, which may or may not have previously been made into TV episodes.
The 2012 adapts the book Anpanman and the Banana Dance (2012), with generous amounts of original material. As always, this will also get a picture-book treatment from the original author, which will be a book based on a movie based on another book of his.
Talking to Himself: With a cast this large, itís inevitable. To name just one example, Koichi Yamadera is Cheese, Kabao-kun, and Kamameshidon, plus a number of side characters.