I have a leakage on my lever, and can't find any Shimano BR-M446s for sale. Was wondering if Shimano BL-MT200s were compatible.
The corresponding lever for the ALIVIO BR-M446 caliper appears to be either the BL-T445 or the BL-M425 (depending on the size; 3 finger vs. 2). You might have more luck searching for those product numbers instead.
The ACERA BL-MT200 seems to have very similar specs to the ALIVIO BL-T445, though based on the angle to the clamp it may stand off the bars a bit further. Specifically they use the same hose kit, SM-BH59-JK-SS, so the hydraulics should be compatible. My major concern, however, would be that the Shimano site explicitly notes that the ACERA part has "braking power tuned for entry level riders."
A leak might just be down to the hose - or fittings - though, so you might want to find out if your LBS can service it for cheaper than getting in new levers.