There are couple of options to do this:
1. One is, if you creating these new company codes with reference to an existing company, and you want to copy the GL Accounts also from source company to target company, you can choose so while copying the company code.
2. Alternatively, you can follow either of these two transactions in SPRO:
a) Financial Accounting (New) -- GL Accounting (new) -- Master Data -- GL Account creation and processing -- Create GL Accounts with reference (here mention target and reference company code and execute it. Then you can collectively make company specific changes, if any.
b) Financial Accounting (New) -- GL Accounting (new) -- Master Data -- GL Account creation and processing -- Alternative Methods -- Copy GL accounts -- Copy chart of accounts / copy company code
Hope it helps.