I think your best bet would be to contact the collection diver(s) directly. If a researcher says "I need an octopus" it is the diver's job to figure out how to catch one and catch it. They are probably the only ones there who might be able to help you. One of the links I posted was for a staff directory for MSI staff. One of those people had the job title "small boat captain". He's probably the diver, so you might want to approach him directly.
If the MSI there is anything like the MSI at UCSB, the people who work there get lots of phone calls asking for random ocean related information, like surf reports, "do you have any dolphins I can visit?", etc. They don't want to be jerks (because they are publicly funded) but they aren't very motivated to do extra leg work researching such questions, so if you don't directly contact someone who knows your answer, you're likely to strike out. Maybe you could specifically ask the woman you contacted to give you the email addresses for the staff divers who do the collecting.
Oh, and it's likely that the collection diver's biggest worries about helping you are:
1) You might be a fisherman who wants to collect as many as you can, for bait, or even for sale, and since he needs to be able to easily find an octopus the next time he's asked, he doesn't want his source to be depleted, so he might not want to tell you exactly where to look.
2) Anything he tells you is a risk to him. For example, you could break some law and say to the game warden, or the judge: "Bob Jones at MSI told me I could do this here".
If you can get him to trust you, he'll help you. It's better to ask him to describe, in detail, what kind of habitat and conditions to look in (depth, temp, rocks or sand, time of day/year, high tide/low tide, etc.) There's no risk in telling you that stuff, and it's easier to trust a guy who just wants to learn, and is willing to do a lot of work on their own. Be humble, grateful, and have a reason for collecting an octopus that they can support. BTW, some people disapprove of traps, so unless he suggests it, you might not want to bring that up (some people don't check traps often enough, or they allow the floats to be a navigation hazard). It helps to ask questions like "is there anything I should be sure to avoid doing? I don't want to damage any habitat or inadvertently kill anything" or "I only want to take an octopus from a species with a large wild population. Are there any species of local octopus that I should be careful not to take?" Anything that makes it clear that you are not a Bozo or a loose canon will increase your chances of getting their help.
Again, if you can get someone associated with marine research or education to do the asking for you, you're much more likely to get their cooperation.
Good luck