Brian, first off please update your profile to show where you are at it can help a little in answering this type of question.
Why is the LO asking for the income approach?
Did the LO request the income approach at the time he/she made the order or was this after the fact. If they made the request upfront you should have significantly adjusted your fee upward to include a rental survey form and Income/Expense form typically I charge $75/form over my normal fee of $400 for each of these forms, does not cover the time required to investigate and obtain information but it at least is something. If the request comes in after the fact (the report has benn submitted) then the fee is $150/form.
Typically what the LO's are looking for when they need the income approach, wtih rent survey and income/expense is "Does the market rent less expenses cover the payment". If not then they will loan less or the deal is dead. They are strictly looking at the income generated to be the primary income source of repayment. Whereas in an owner occupied home they look to the income from client work as the source of repayment. Hope I made sense of that for you.
Sounds like you need to do some talking to your LO to find out why they want the income approach.
Now, as to where to find and develope the data, much of that is going to depend on your local. If your local MLS does not have information on rentals then it time for the old fashion way or developing comparables, personal contacts and shoe leather. Check your yellow pages for property managers visit with them to find similar physical homes that they are renting. Check the local for rents in the newspaper. Drive the neighborhood looking for "For Rent" signs and call about them. Talk to other more experienced appraisers in your area they may have some rental comps or tell you who to talk to.
As for the income/expense form, request the past 3 years of tax records from the borrower that shows the income and expense. If they use a property manager then there should be an annual itemized statement from the property manage and of obviously they will be your best source of rental comparables.
Last question, are you a trainee. If so you need to be talking seriously with your mentor, and if they cannot help you find a new mentor. I cannot believe that any appraiser would have gotten through the training with a good mentor where the use, and whys and how to do a rental survey and income/expense form was not completely taught. Typically for my trainees that comes at about 1/2 way through their training cycle.
Good luck hope some of this helps you.
To given you some insight primarily in owner/occupied single family residential the income approach as you state typically is not required to be produce a creditable report since the market