Aye AJ,
Welcome to the '......... house'!

I have been running a SRX600 1JK 'Sally' since ~2005, with no rubber sheets or the side cover into the air filter and so far no problems with standard carbs, a BSM 'Futura' aftermarket exhaust, iridium spark plug and a K&N air filter rather than the Yamaha OEM air filter. Image attached.
This is the filter on the K&N UK site as of today 10th August 2018, don't know what the exchange rate for the C$ to the GBP is like but maybe worth a look?
Link:
Yamaha SRX600/400 1JK K&N air filterDON'T excessively oil the filter!
If you want to make up a replica of the rubber sheets that fit behind the alloy side cover, then I suggest that you might use 1-ply Insertion rubber sheet, either 1.5mm or 2.0mm in thickness. Draw and cut out a card template, then trace around on the rubber sheet with a soft (2B) pencil and cut out with a good sharp pair of scissors. I don't have a template for the 1JK ones!

I suspect that there is no need to emphasise the need for clean oil and oil filter and to be aware that 30 year old oil seals, especially in the oil pump, may not be as pliable as they once were.
SteveH, who's site 'SRX600.net' is, also looks after this site and occasionally comes in on site, as does SteveL, who has a rake of these beasties; Ian also has plenty of experience rebuilding them as well. If you keep the 'Bike Problems/Questions' board selected and then enter SRX into the 'Search' window in the top right of the board page, you will select a whole raft of problem solving, crying into workshop rags angst and pats on the back!

We may not have seen it yet, but there is a good chance we have.
If eBay cannot come up with the goods, then you may have to speak nicely to the Japanese community in Vancouver or go directly to 'Jauce', the Japanese equivilent to eBay, where all this stuff is obtainable, but may cost you!
You should also know that a lot of the Yamaha Raptor 600 snowmobile engine parts fit the SRX motor, I am running a Wiseco barrel 'Standard' (598cc) bore sleeve and piston in my 1JK motor for a Raptor.
Good health, Bill
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