Apart from all the ways already mentioned, the easiest thing a commercial bank can do to increase its bank reserves is to just sit and wait.
Every time the government spends, it instructs its central bank to credit the reserve balances held by commercial banks at the central bank (and as is often necessary for eg. pubic sector salaries, the commercial banks proceed to credit the deposit balances of the final beneficiaries).
Sure, tax collections returning to government will result in reserve balances being decreased but as I'm sure you know, most modern governments run a current account deficit each year. This means more reserves (and deposits) are spent into the system than are taxed back out of it.
But why would commercial banks want this? Usually they would much rather swap their excess reserves with government bonds which the government is all too happy to issue. These usually pay a greater interest rate.