Update values on 1 sheet with values from multiple source sheets

Hello
Here's my problem. I get a daily report where I need to update the values in a particular column (set at zero) with corresponding values from multiple source sheets.
In my attachment, on the Main sheet, I need to update the values in column N with the relevant values (corresponding Trade Refs) in Source A and Source B sheets.
e.g. Main Sheet N1 should = £1 (from Source A) & Main sheet N2 should = £12 (from Source B)

I want to be able to achieve this with a click of a button.
I've been able to achieve this with an Index & Match formula but only for 1 set of source data, I can't get the ranges to cover multiple sheets! I've been trying for ages and its been driving me mad! Obviously, I am an excel novice.

Can anybody take a look? I imagine its something quite quick for an expert.

Thank you