Hello Bagface
Based on the manuals I have you need to remove the steering wheel column covers, the cluster finish panel, instruments, airduct #1, and the cluster finish lower panel to get at the master cylinder.
If you want more details on manuals etc have a look at the long first post in my show us yours thread (same username) for links and options.
If you can find a kit (from Toyota, I’d suggest) you can service the master cylinder or put in a new replacement. If the cylinder is scored or otherwise damaged a new cylinder is a no-brainer. A new unit could be from Toyota or a good parts supplier. I might be tempted to go OEM. It is the brake master cylinder after all!
Rebuilding or replacing is not a hugely difficult job. It likely depends on how urgently you need the van back on the road and how confident you are to carry out the necessary steps and subsequent fluid work and bleeding?
I’d also be wanting to check the vacuum boost and general arrangements. Is there an obvious leak or some specific reason pointing you to having to replace the master?
Timmy the Toolman on YT has several vids on Toyota brake master cylinder work.
I understand the pedal height (its top) from the floor should be 151.5mm
All the best!