Ok, So we have the Copper Chromite dehydrogenation of BDO, the semi-completed GABA/Nitrite, but how about some more novel routes to GBL...
The Australian government has recently taken steps to begin to restrict these following chemicals in an effort to fight GHB.

4-HYDROXY-BUTANOIC ACID NITRILE
4-HYDROXYBUTANAL
2-HYDROXYTETRAHYDROFURAN
2-PYRROLIDONE
4-HYDROXY PENTANOIC ACID
4-HYDROXY BUTANOIC ACID LACTONE

Do any of these present a viable starting material?

The first four are only a theoretical hydrolysis or oxidation step away from GHB. I doubt that it would be very easy in practice, as both ends of the molecules will react to varying degree in whatever procedure you use on them. Most of the substances seems to have become regulated from a theoretical standpoint only, as they are generally too expensive, too unstable and/or directly impractical to use as staring material for GHB/GBL.

The latter two are synonyms for 4-Hydroxyvaleric acid and gamma-valerolactone, respectively. More reading on those two substances can be found here:

https://www.thevespiary.org/rhodium/Rhodium/chemistry/4-methyl-ghb.html

Edit: I misread the above - the last one is gamma-butyrolactone, not gamma-valerolactone.

The latter two are synonyms for 4-Hydroxyvaleric acid and gamma-valerolactone, respectively.

Isn't 4-hydroxybutanoic acid lactone, in fact, gamma-butyrolactone?

Post 439780

(Aurelius: "Compilation on GHB/GBL", Methods Discourse)

why did I bother?

the gaba route is so simple, i can't believe no one with access to analytical equipment has been able to analyze the product =(

I am considering doing the gaba to GBL via NaNO2 when i get some lab time, probably not till the summer but I want a final workup from chromic anyways. I have access to GC/MS, NMR and IR but no lab to work in except on vacation. Really sucks the way things work out...unless another bee wanted to mail me the sample? lol
~Hester18

Hehe you poor bastards, bugger making GBL.
Lucky for some ppl GBL can still be bought.  
$500\2.5L isnt great, but price has gone up since Oz government made it a scheduled precursor  
Who wants Na-GHB though? Definately not me!