A 1031 exchange is considered a like-kind exchange, and as such, allows you to defer recognition on a gain or loss that might occur as a result of the exchange. Since a 1031 exchange is a tax matter, a CPA or a CPA firm would be an excellent place to start. If you can, reach out to a CPA or firm that specializes in 1031 exchanges or real estate taxation. Since real estate taxes are a very specialized form of tax practice, I would recommend reaching out to a CPA or firm that specializes in tax consulting. CPAs and firms that specialize in tax consulting tend to have an extensive knowledge of tax law, and they often work directly with clients in planning the tax benefits or consequences of major transactions like 1031 exchanges. Tax consulting and planning is a service many CPA firms offer, and they should be able to connect you to the right professionals if they are unable to help you with your 1031 exchange.
As to a middleman holding funds, a 1031 exchange is a like-kind exchange, so there are some specific rules about how long you can wait between selling one investment property or business and buying another similar investment property or business. As far as I know, you do not need to use a specifically designated middleman to hold funds between exchanges, but a CPA or CPA firm will be able to advise you as to who should hold funds for you if that is required. Generally, the rule is that you must use the proceeds from the first sale within 180 days to purchase a new property or business, but you are required to identify the property or business you intend to purchase under the 1031 exchange within 45 days of the first sale. A CPA or CPA firm will be able to advise you as to the application of the 1031 exchange rules and how they will specifically apply to your case. A CPA or firm should be able to offer a lot of general advice on the specifics of 1031 exchanges.