I need a buttplate for a 60s era 39A.  Anyone know where I can find one or if other Marlin buttplates will fit?

Thanks in advance

Most plate sold these days are replicas.

Here's some good sources.  Note that over the years Marlin used a number of designs.
If you need white spacer material, you can buy white plastic sheets at most hardware stores or the below sources usually have pre-cut spacers.

http://www.gungrip.com/items_154__marlin%20buttplates.html

http://www.vintagegungrips.net/mabu1.html

https://www.gunpartscorp.com/Manufacturers/MarlinGlenfield-33379/Rifles-37333/39Series-38980/39ALateModel-34039.htm
(May or may not be original Marlin made).

http://www.jackfirstgun.com/
(Probably original Marlin)

http://www.poppertsgunparts.com/cgi-bin/webdata/webdata_gunparts.cgi

The white spacer can be cut from an empty 5 gal bucket.

I have the spacer. Thank you for the assistance.

Back in the early 80's my buddy and I fitted our 39-A rifles with crescent curved brass butt plates.
These looked really nice, but you have to be careful in fitting one to make sure you don't wind up with the stock too short.

After that, I fitted several other 39-A's with Neidner checkered steel butt plates and grip caps.
You can still by Neidner plates and caps from Brownell's, but they're made by a different company.

http://www.brownells.com/rifle-parts/stock-parts/butt-plate-parts/butt-plates/neidner-butt-plate-grip-cap-prod332.aspx?psize=96

Brownell's also sell a variety of brass and steel butt plates, some are rough parts that need to be finished.
However, many of these curved or checkered plates and grip caps add a very nice touch to a Marlin.