Scratch Paper

Vendors do sell mock noteboards, like this one here: https://www.testdayscratch.com/

You will get a pad of 5 laminated pages spiral bound together. They are approximately legal size (8.5" by 14") The first page has instructions on it, so you effectively get 9 pages to work with.

There is a watermark grid on it which is effective for chart questions, or making your own chart as you described, but for the most part I ignored it.

For the AWA, I do my planning on the actual screen.
For the Verbal, I don't use my noteboard for the most part, but for tough ones I will use a chart that looks something like
--1 5 7
A X
B X
C
D X
E X

I only fill in the number of the questions on the top column as needed, and I would actually draw the column and row lines.

For Math I am not organized at all.
I might write a 15 and circle it to indicate a question number, and then write an a) b) c) if i'm working backwards and trying to solve for each possible answer.

For the data sufficiency ones I sometimes will
1) sufficient
2) insufficient

or something like that

I highly recommend practising with a dry erase marker and some sort of similar writing surface, like a whiteboard.

Agree with the above. I didn't write much for AWA, and didn't have much scratch work for verbal either. For data sufficiency I used the A D / B C E method taught by the Princeton Review, and I used the board to scribble for that. For PS, obviously I used the board to work out problems.

I tried looking for the board but couldnt find any nearby and don't think i have the time now to figure it out (i travel a bit for work) - so was wondering, is it a disadvantage to not have practised on the scratch paper?
Is there something similar that I can substitute at home?

I never practiced with the whiteboard/dry erase -- I generally used a PEN and white sheet of paper. I think it might help but it doesn't hurt you if you don't. Just don't erase while practicing, since you won't be able to on the test.

You can buy dry erase markers and whiteboards almost anywhere. It doesn't totally simulate the experience and gets very messy (you have to erase a lot), but I found it very helpful in preparation for the real thing.