Also you can ask for a flair here
I buy pens from Reddit.com/r/pen_swap, fountainpennetwork.com (free membership, also discussion site), fpgeeks.com/forum/ (free membership, also discussion site)
fountainpenboard.com (free membership, also discussion site) and from various restoration and specialized brand websites. You are welcome to post a pen here to sell or post asking for a pen.
If the pen is not in good cosmetic shape or stuck together to badly, these places can fix them for you. It is mostly ordered by price.
Do It Yourself
I would recomend this for a pen that: is a lever-filler, not worth more than 100$, has only light and not noticeable scratching, and you are comfortable with breaking the pen. Otherwise, trust a professional.
He is by far the cheapest and I definitely recomend him for the average user. He is a good restorer who is not in it for a profit. I would send it to him if it is not a really valuable (monetary or sentimental) and you don't expect it to be polished with unicorn fur.
Can repair almost any pen at a very good price. He is pretty much the next step up in quality and costlyness, You are paying more for work that is more complicated and in-depth.
Sean Nicholson AKA "Write on Time Vintage Pens Restoration and Service" on facebook this is going more into restoration for expensive and rare pens. His prices are more than Dahl's but he does more and will be able to restore older and rarer pens. He will also barter and might trade other pens you have for the restoration or alter his prices. He sells a few pens as well.
He is one of the best pen repairmen and also sell parts and supplies to repair your own. He is very active giving advice on sites like fountainpennetwork.com and is very knowledgeable and skilled. He sells lots of pens for very good prices on his website and has an extra section for supplies and discounted pens. His repairs are very good and can do very complicated things that most do not even try.