Substitute for Accent Seasoning

Accent seasoning seems to be mostly Monosodium Glutamate (MSG). You can try to find another MSG-type seasoning in your normal store (I don't know what brands might be available where you are so just look for things with MSG as the main ingredient), find pure MSG which is sometimes available in Asian grocery stores, or you could just add a cube of bouillon or two to help round out the flavour a bit.

MSG basically tastes a little salty and helps make the flavour fuller or more intense. Bouillon does the same thing, so it would be an acceptable substitute in most dishes.

"Accent Seasoning" is Monosodium Glutamate (MSG): It looks like salt and is predominantly and originally, but not exclusively, used in Chinese & other East Asian cuisine. It's a 'flavour enhancer' in the same way salt is and has a similar but not identical purpose.

Look for an unbranded variety (supermarket's own, etc). It's very much like salt & isn't much more expensive unless it has a brand name attached to it.
There is nothing "special" about branded versions, like buying a brand name at $£€ 3.00 instead of supermarket paracetamol for $£€ 0.30

If you can't find MSG, regular salt will do at a push, [though it is not the same], at about 1:1 ratio... though to be wise, start with less. You can always add more at the end, you can't take any back out.