New joiner but long term enthusiast. I hauled back a Pioneer CLD-99S from Japan (along with a copy of Akira!) from Japan last jaunt.
Long story short - my partner plugged it into the wrong power adaptor (not step down - Australia/240v mains) and blew the transformer.
I'm not super savvy, but had an electrical engineer test to identify that it was indeed the transformer but he's no ideas on replacement parts.

Is there anywhere I can source a replacement? I've trawled through the forums that seems to suggest my best option is to find a parts only unit and play Frankenstein.
Is this the only way? Is there an equivalent 240v unit that is compatible? It seems I could also get a CLD-3030 and shift my region problem to US...but would appreciate any insights from someone who's rocked this process.

CLD-3030 power supply is not compatible, so you will need to get one from a parts CLD-99S. There could be further damage in there (i.e. the audio board).

Would it definitely be the whole transformer blown?

I don't know details about LaserDisc power supplies, but I recently had to fix a similar issue with a (modern) Japanese device that had been plugged into the UK mains.

This had a 'Metal Oxide Varistor' across the main power supply. When 240V came in, it did its duty and shorted out the power, nobly destroying itself but also causing the adjacent fuse to blow, and protecting the main device from damage. Fixing it was just a case of replacing fuse and varistor.

Is this a recent innovation, or would an older device like an LD player have something similar?

There are some ceramic capacitors that look similar to MOVs on a small board before the power board. Glass fuses are located on the secondary side rather than the primary side as with later models. There could potentially be a thermal fuse inside the transformer itself.