As Ricey said, polishing every two months is massive overkill, even with a DA.
The best thing you can buy for the Silverline is a bin to put it in.
Your "need" to polish every two months is down to two things;
SRP isn't a polish (despite its name), it's a glaze at best and bloody awful to work with IMO. It has very little, if any depending on which version you're using, cut itself but is full of fillers. Thus you're not actually correcting anything. You could use it with your polisher if you bought a finishing pad with no cut, but SRP is even worse by machine than it is by hand, ESPECIALLY with a rotary!
And/or your wash technique needs addressing as you're inflicting more swirls more often. The correct wash technique will ensure that you need to polish as little as possible.
Either way, a Silverline rotary polisher isn't the right answer.