I've considered that option but am hoping to keep it "original". ThanksIf I remember correctly that model has a 3/8" dovetail on the top of the receiver.
You could add a scope like this-
rimfire riflescope Simmons .22 MAG
OUCH! Maybe a scope is in my future ThanksHere is one on eBay
Marlin / Glenfield Model 99 M1 Factory Rear Sight, 99M1 | eBay
Marlin / Glenfield Model 99 M1 Factory Rear Sight, 99M1.www.ebay.com
As per recommendation by Equalizer, below is a link to Sarco's website with search hits results for a search of "Rear Sights" (it kept truncating longer search strings I tried). There's several pages, so you may want to call them, but to can also looked through the results (or have better luck with your search strings than I did). Good Luck:On an outside chance. Call Sarco, located in Easton, PA
610-250-3960
Good luck
They have the base not the leaf. I think I just purchased the last complete sight in existence. But the guys who had mine actually have another one that is complete but taken apart. Outback Gunparts in Indiana. I gave $95 for mine but it's in excellent condition.You can probably find what you need in the link below for your Marlin.
It looks like they have the rear sight in-stock.
Marlin/Glenfield Model 99M1 Parts | Gun Parts Corp.
Find Marlin/Glenfield Model 99M1 parts and schematics today with Numrich Gun Parts.www.gunpartscorp.com