I think you have two questions wrapped up in one. First, Good advice from Judy Jones. Find a loan broker that is a direct underwriter for FHA loans. This just makes the process easier. Then see if they have ever done an FHA 203K. You really need an experienced loan officer to do these as there are many i's to dot and t's to cross. There is a delay in paying contractors so this becomes an issue. If contractors are waiting on their money, they will usually charge a premium for their services. It's just the cost of doing business. There are also many specifications that need to be met. A very doable loan, but never easy.
I might ask, why FHA 203k? It is much easier to structure your rehab with other financing. Construction loans, equity loans, lines of credit, etc. Money supply is tight but there are financial institutions who will work with you if you have good credit, a track record, or some business plan for your rehab. Check out credit unions, local banks, savings and loans. Many offer various types of financing that is outside the box of conforming loans. My experience is they are usually conservative, so good credit and cash invested is preferred. Home improvement stores also offer special credit for materials for rehab projects. If your starting out with no cash and little credit. It might be tough getting started.
Second, I don't think there is such thing as a 203k purchase. HUD advertises their foreclosed homes that qualify for 203K financing, meaning they need work, but 203 k financing is a term for just the loan. You can use 203k financing for any home that qualifies and needs rehab work, not just the HUD repos. 203k is just the financing instrument. If you are looking for homes to fix up, yes, I recommend finding a realtor who can assess various homes for sale for their feasibility. There are lots of homes that can use fixing up, but I have seen many good intentioned rehabbers get upside down on a project. They buy too high, invest too much, and then have a beautiful home that is overpriced for the market. I might also suggest looking at VA repos that offer financing. Some of these are very attractive purchases. The VA just adjusted their program to 5.75% financing and do not rely on credit scoring for financing. I have details if you are interested. Check my profile for contact info.