An "ocean drum" might be an interesting idea, rather than just an overlay of a literal ocean. I think producing these kinds of effects with instruments rather than pouring on the FX is a bolder artistic choice, if the client is persuadable. Ocena drums are cheap, and a fun instrument to have around. It's essentially a flat, two-headed drum, about 15" in diameter, with BB's on the inside.
The secret to playing it is to look through the clear side, and to roll the drum around, watching the BB's rolling around inside. By varying the speed you roll it, you will quite literally see waves made up of the mass of BB's cresting, just like ocean waves. It takes about ten minutes to perfect the technique. Once you learn to make really realistic looking "waves" in the BB's you discover that this is reflected in the sound you're getting. Very calming to play as well.
VSL has an ocean drum sample which is very nice, but this is one of those instruments that is cheaper to buy and record yourself, not to mention being more fun.
That's an idea, at any rate...
Having worked with both Sound Ideas and Hollywood Edge extensively, I tend to favor Hollywood Edge's ambient recordings over the Sound Ideas recordings. Be sure to check the edition of Sound Ideas, when you're working with those. The early series of theirs are primarily analog recordings, and they tend to be hissy and noisy. I think it's the 6000 Series forward which are the more pristine of the bunch. Hollywood Edge has very few noisy samples, they're all pretty high-quality. The only minor complaint I have is that they tend to overfill their ambient bed tracks. There's a "country birds" ambience, or something to that general effect, which sounds like the invasion of the entire world's bird population...a bit over the top for most applications I've ever run across.
If you're just looking to license a single ocean clip, though, I'd recommend SoundDogs.com. Open an account with them, and you can audition and license sounds on a per-minute, flat-fee basis. I know they have most of the Sound Ideas library there, if not all of it, and also many, many others. They have a great interface, with low-res MP3, etc., audition buttons right there on the search results. You just check the sounds you want, proceed to checkout, and they e-mail you a link that's good for a certain download period. I've never had a single problem with them, and I use them for some little something on every show I do. Once you've licensed something from them, you have a lifetime license to those sounds, no matter how many productions you ultimately use them in. So, it's a pretty darn good deal, I think.
Have you searched for soundfont files (SF2). You can do a search on Yahoo for these files, and eventually you will find numerous sites with free Sf2 files. Some, not so good, but some can be useful specially for ambient noises. I have a couple of ocean wave SF2 files, not sure where I got them from. It's Ok for little ambience effects and add-ins here and there. But I would not recommend using SF2 for any primary music productions, as you may get what you pay for (Its free)
This past year I had to score a movie that was centered around the sea shore.
I also had to help with sound design and I had the same inquiry then.
I ended up using a bunch of different sources...
There is one cool ocean patch in Atmosphere that you can either use for soft waves or very angry ones, depending how long you sustain the notes and what the velocity you use: Noises/Morphing Noise/Sea Foam