Any suggestions for the best drive chain lubricant for an unsealed drive chain?

Any boil in the tin chain grease.

As tinkicker said BUT use candle wax!
Degrease chain the dry and boil.

I hang mine up and torch it so the wax melts into the chain.

Once cool shake off and install.

Do not lube after!

I wonder how the carnuba wax for bicycle chains would work?

Joe Lunati would simmer his SC500 chain in  STP

Back in the "70's we all had "Duckhams Chain Grease" in a large low-ish tin, like a big biscuit tin.
Would sit the chain in & heat it up.
Can't remember how i heated it but probably waited until wife went to town then stank the house out.
Maybe i sat that tin in a bigger pot of shallow boiling water to melt it all.
Then would hang the chain up draining back into the tin.
Then repeat after next motocross.
Found a pic of one sold on Ebay haha so still around or vintage collectable still around.
photos.app.goo.gl/nMn64KaSRqd8yApQ7

Yep.  I used to get a rollocking off my mum for using the cooker in the kitchen. remove chain, scrub it with parafin.  Put a bit of wire through the chain end link to use to extract it from the simmering brew and hang it up from, then dunk it in the melted mess for 15 mins. 
Remove chain and tin from heat, carry it into the garage and hang the chain over the tin to drip dry.  Result, one brand new looking chain.

In the UK we had Duckhams, but I used Linklife chain wax.

Still get Putoline chain wax over here, but the tin does not have a carrying handle.  A serious oversight in my view.

www.dirtbikexpress.co.uk/products/putoline-chain-wax-1000g

 

Haha, memories eh!!. What would we do without them.