Baseball, do a search for "repairing pitted hydraulic cylinder barrels" on google. There's a ton of info out there.... But differing solutions depending on the amount of pitting and just how deep the pits are. And how much life you want out of the cylinder.
A bit of a summary for you:
Solutions to repair the pitting:
1. Epoxy filling and re-honing the barrel. For epoxy to work properly, the cylinder must be ABSOLUTELY clean, as the epoxy will not stick to oily steel. There is an industrial product called Belzona 1151 that might do the job for you. The Belzona line of epoxy products is heavily supported by technical people who will help you with details of doing the job properly and, more importantly, tell you if their product is routinely used for this kind of repair.
For the re-honing of the barrel after the epoxy repair, I would be inclined to go to a shop that has a proper cylinder hone that can be set to a size. However, I have seen people post that they just used a spring type hone to get the epoxy back down to the barrel size without trouble.
You may have a nearby hydraulics shop that would do this type of job for you for a reasonable cost. They probably have done the procedure in the past so they will know what works and what doesn't.
2. Some people have talked about TIG or MIG welding up the pits in the bore, then cleaning it up by grinding the high spots back out and finishing up with a precision hone. Lots of work. Good for the guys who are making a living with the cylinder.
3. Get a new piece of cylinder barrel and have a shop re-barrel the cylinder. Involves lathe work and lots of shop time but may be less costly than a replacement part.
Non-repair solutions:
4. Find a good used barrel.
5. New part, brand name or aftermarket.
Further to fixing with epoxy material:
The concern about an epoxy repair failing and sending crap down the line is real but can be offset by using "compact pressure filters" in line with both end of the cylinders. These are small filters about the size of a pop can that contain a metal filter like sintered bronze and filter down to about 25 micron. They are available for the pressure ratings necessary....3000psi or therabouts?
YMMV.
Jon.