If you want to take a look at the source code for the version of Microsoft BASIC that came with Wales’ most famous computer then you’re in luck.
This GitHub repository contains the source code for the Dragon 64 versions of the Microsoft 16K BASIC Interpreter for the Motorola 6809 (aka BASIC-69 and Extended Color BASIC).
The source was recovered from a paper listing of the Motorola assembler output that was produced in 1983 at Dragon Data’s R&D facility near their Kenfig factory in Port Talbot, Wales. The shared and unique source for both the 32K and 64K mode ROMs are present, and despite being boxed in an attic for a majority of the previous 39 years, the listing is very well preserved. It totals 340 pages of fan-fold tractor feed across 4 bundles.David Linsley
You can check it out here