Your Marlin model 44a was made from 1923-1935.That being said I would probably discount finding a original manual from Marlin.I do believe that ther could be reproduction manuals printed/copied that might be available on either E-bay or some publishing company.Good luck!
On the main Marlin Firearms website, there is a section labeled "Owners Manuals", from which you can download the manuals of Marlin products in .pdf form. Assembly and disassembly instructions should be included in these manuals. See related link.
You can go to Marlin's home page and print one from there. I printed one for my model 60. It is in Adobe format.
The JC Higgins Model 45 was made by Marlin and is basically the same gun as the Model 336. Manuals are availabe from Marlin Firearms. The JC Higgins Model 66 was made by High Standard and is out of production. I have a manual scanned, and can email it to you. sales@countrygunsmith.net
Marlin 336 Owners Manual at Marlin Firearms website: http://www.marlinfirearms.com/pdfs/manuals/MFC_Centerfire.pdf
The marlin model 39A is the rifle model,while the Marlin model 39M is the carbine model.
model 55 the original marlin goose gun
Marlin 81
The Marlin Model 60 manual may be dowloaded from Marlin's website.
The Marlin Firearm company has owner manuals for the different firearm models that they sell. You can find downloadable versions of the manuals on the company web site.
The Marlin model 925 22 long rifle, was first introduced in 2003. Before that it was Glenfield Marlin model 25 or just Marlin model 25. Hope this helps.
The Marlin model 80G was a promotional model that was made from 1960-1965.
The marlin model 995 was made by marlin between the years 1995-1999.