A couple of thoughts ... that have nothing to do with the report you want.
1) If the previous owner, or owners, performed basic maintenance (oil and filter changes, wheel rotation, etc.) themselves, that will not be in any report.
2) One can only assume why they will not share whatever service information they may have available (it's incomplete or there is something "big" in there or that has not been performed). I would ask whether the information you want is available to them. If you know as a fact that it is, and they tell you that it isn't, they are not being honest and maybe you move on (that's no way to begin a relationship).
If they simply refuse to provide the information, I would again assume - that there is something they don't want you to know. This puts you in a position of power, as they clearly want to sell it to you and are hiding something (this alone may be a reason to move on).
You have to understand the mindset of sales. They try to hook the customer and they are pretty good at recognizing desire and pouncing on it. What you have to do is demonstrate that you are willing to walk away (this really is no different than bargaining in a "tourist trap" - you have to be willing to walk away).
Explain that you are interested, but won't buy unless you have what you've requested. Ensure that they have your contact information and calmly say "You have my contact information; when you're serious about selling, please let me know.", and walk off with confidence. Of course, keep looking.
