Welcome to the forum, please do some pictures.
Cleaning rods are difficult to find problem free, expect to pay $50+ for a good one, if you can find one. Best bet is ebay, Gun Broker or another collector, but collectors rarely will sell one, you will need a trade in most cases. Problem is that most collectors have more rifles in need of a rod than excess rods, only MauserBill has the reverse situation and he won't sell them, he only trades.
MO/1915 isn't rare as you guessed, but nice original ones are a lot tougher than you would think. Rifles made in 1915 were used, there was a rifle shortage and most made found their way to the battlefield. Generally 1917 is the most common date to find nice and original, regardless of maker, they are usually the most common rifle to find from any of the makers.
During 1915, Danzig & DWM had the highest production, Spandau a close third, basically tied with Mauser, the balance of the makers were smalls by comparison.