Hi Gaetan
I purchased a set of genuine conrods (complete with bolts, nuts and small end bushes) from VWHeritage back in 2015 for about AU$270 + freight. They are identical in every way to the existing rods, and at the time it was cheaper than buying new bolts and having the old rods measured for straightness, closed and honed, re-bushed and reamed.
As for the availability of parts, it is better now than it was when I bought my first WBX back in the 1990's. There's very little that you can't get, and what you can't get can be made. I don't know if you can say the same for a Subie in twenty or thirty years time.
At the risk of offending others, I won't ask if the Subie-engined transmissions will last that long - they were originally designed to handle 68 BHP in a 1973 1700 kombi.
The WBX engines only get a bad rap when they have been abused by lack of maintenance or improper coolant. They are an incredible motor that lasts for extremely high mileage, and unlike most 'disposable' modern engines, don't have to be thrown away when they wear out. (Think about the cost of replacing two or four cams, instead of one).
The WBX has the capacity for three crankshaft regrinds. With proper care they can be rebuilt several times and last for many more decades.
Don't think of it as a slow car. It's a fast house.
Cheers,
Roger.