Yes, syringaldehyde is the topic, and I guess I didn't make myself clear.
What's being proposed is taking a big pile of saw dust or wood chips or whatever, soaking it with acetone, then pressure cooking it with lye, nitrobenzene, etc. (incidentally, every pressure cooker I've seen has been made from aluminum; if anybody attempted to fill it with nitrobenzene and lye and heat it under pressure, imagine the mess created when the lye corrodes the walls of the pressure cooker and hot, semi-explosive nitrobenzene comes shooting out all over the place.) When the reaction is complete, you're left with a great big stinking mess (don't forget that aniline is generated in the reaction, since nitrobenzne is both the solvent and the reagent) that you'll need to do a work-up on, first to extract the aldehydes, and then you'll need find a way to efficiently separate vanillin and syringaldehyde. In the end, which would be a long time from when you started, under ideal conditions, you'll be left with a huge pile of waste to deal with, and hopefully a tiny pile of your final product. This seems entirely too messy and too complicated, especially considering the amounts of syringealdehyde that may be needed later on, depending on how ambitious a person is.
What I'm suggesting is this:
Vanillin -> 5-bromo- or 5-chlorovanillin -> syringealdehyde.
I believe this to be the more sensible alternative. Vanillin is brominated or chorinated using hydrogen peroxide, acid, and an appropriate bromide or chloride salt. 5-halovanillin is methoxylated using sodium methoxide and copper salt catalyst in ethyl acetate. Yields are good, details can be found on Rhodium's chemistry page.
Yes, it's not purely OTC, but then again I haven't found a OTC source for nitrobenzene or chloroform around where I live either. In any case, the chemicals for the vanillin->->syringaldehyde route are not especially unobtainable. The reaction volume is going to be much, much smaller, far less waste is generated, it will cost less time and money, and it doesn't involve anything like heating a caustic slurry of sawdust and quasi-rocket fuel under pressure...
But hey, if that's your thing, don't let me limit you. If you really, really want to challenge yourself (all the while endangering yourself, your lab, and any of your closest neighbors), don't let me take away your dream. Just be careful; that's all I ask. Yes, be careful, and don't do it anywhere near me.