Where I can buy an extra reservoir for the sc circuit like the evosport one?

I'm pretty sure Evosport uses a power steering reservoir from a BMW.

You can go to Meziere's website since they offer overflow tanks but it depends on what size you are looking for.

Good luck!

I bought one like BrianS uses in his DIY. Nice for 3 reasons: price(got mine used off ebay with cap and bracket for $20; the outlets exit at an angle rather than straight down;and the heat resistant material it's made from. A metal reservoir will become hot from underhood temps. It's from a Saab 9-5. Probably lots of other models too. All you need to hook it in to circuit is a 5/8 to 3/4 reducer hose barb connector. The part # on the reservoir is PA 66 GF 25. If you're sourcing used, make sure it is sold with cap and bracket.