Using Microsoft Access for databases of tradestands. Is there a better way?

It sound like all these attempts to integrate different databses with each other are causing a problem, I don't think using a different program will help you as it will require learning how to use an entirely new package. I think brushing up on your database theory is the best option and rather than attempting to integrate these various databases, creating a working relational database, by working from this master database you referred to and customising it apropriately you could avoid the need to create additional databases and avoid the requirement to attempt to integrate them, good design should be the first thing you aim towards. Access is designed as a relational database and there is no reason you can't store all this information under one file, create a well planned correctly normalised relational database in access and you could probably drastically reduce the time you spend on admin. Using well thought out structure, forms, queries and reports should solve your problem.