Help me to locate...

[Nighthawk]

... a source for historically accurate trews, please! I can't seem to find them anywhere! Great kilts, yes. 1700's style trews? No. Any help would be great. Thanks!

[Chef]

Try HERE. I believe they will make them on the diagonal for an extra fee.

[Pleater]

Close fitting garments cut on the diagonal are very different from those cut on the grain of the fabric.

I have not worn trews, but did make myself a jacket with very narrow sleeves all cut on the bias, and found it could be fitted much closer than the same pattern cut straight. The sleeves were much less binding and the jacket gave much more freedom of movement.

It does take more fabric to lay a pattern on the bias and also to make trews without a side seam. It would also be even more extravagant if the tartan was asymmetrical as pattern pieces could not be laid in opposite directions.

They do need lining. Close cut, they leave very little to the imagination. I don't think it was quite so shocking when they were first in fashion, but these days we are not used to seeing quite so much detail.
No wonder the ladies needed fans. to cool their flushed cheeks.