Almost any hydraulic shop that deals with metric sized cylinders should be able to help you. If you disassemble the cylinder and get measurements of the cup seals, wiper seals, and O-rings, you can probably order the parts online yourself. These are all off-the-shelf components.
Yes check with Midway as they have a good range of parts. I have bought seal kits for my backhoe cylinders from them before – they even threw in some extras for free so now I have spares.
They will be hearing from me shortly as my dozer has just snapped an axle.