There were plenty of magazines (Print) in the UK & Germany that featured arranger players, demonstrators and concert artists which explained a lot of their work, they also produced articles (And still do) for the customers. (The most well-known for Yamaha in the UK is the Yamaha Club who regularly feature articles on style creation by top artists (As well as having their own festival)
There were various ones for both Korg & Roland as well as others, and of course general keyboard magazines that featured both organs, (The organs easy play features were where the arranger keyboard stemmed from) Pianos and arranger keyboards. (Keyboard Cavalcade (Print) is probably the best known in the UK)
Various forums are available for most manufactures that are still around (Sone like Roland.com have gone due to low demand) where help is available. (If you do a search you will also find various podcasts that have sections that feature arranger keyboards with Community keyboards in the UK being quite popular)
There are many other countries as well if you do a quick search on Google. (I also did a quick search for arranger style creation on YouTube and a number of videos came up straight away)
In the UK (And Europe) there are also many festivals that feature arranger keyboards were you get to talk to the style creators as well as getting live demos of how to get the best out of the keyboards.
As you can see there are plenty about if you don’t mind paying for some of them (You can’t put a price on Knowledge) by just doing a general search. (The US is a problem as arranger keyboards are so minute compared to other countries there is no incentive to bother with them. (That’s the reason most magazines and sites are run from Europe and Asia)

Bill