Hilton Head Area

Most HH timeshares are not on the beach. There are far many that are on golf courses than ocean front. Marriott has 4 that are oceanfront or very near the ocean and fit your description but the time you mention is gold season and still fairly popular. II is much more likely than DAE to get you one but it still may be a difficult trade because other Marriott owners have priority. Marriott also has 4 that are not ocean front but are in harbor settings (Shelter Cove and Harbour Town) which are very nice and easier to exchange into. They are smaller resort that were mostly developed before Marriott and don't have all the bells and whistles like multiple pools and restaurant/bars, etc.

Waterside is nice but is 2-3 fairly long blocks from the ocean.
In my experience SFX is not particularly strong in hilton head but does get a few deposits. Island Links and Coral Sands are about 5 blocks from the ocean (more golf course-y but nice). There are several others. Between tripadvisor and the review section here they are pretty well covered.

I think if you go in October or early November you have a very good chance of trading into one of the Marriotts. We go early November every year and love that time of year, but you will need a heated pool! We love our unit at Port o Call, but it's a couple of blocks to the beach. I like the location of Grand Ocean the best of the Marriotts, but they're all nice!

Try SeaCrest

We love Seacrest Surf and Racquet Club...one block from the beach, but access to the Ocean Front pool at SeaCrest makes it a good bargain. Most units have 2 condos, full kitchen, 2 bedrooms, elevator, free parking It is right across from Coligny Plaza, so you don't even need a car once you get there.
October is our favorite time of year. It can be very hot and summery or just right, but there are no crowds. Our favorite place to be!

http://seacrestsurf.com/

Marriotts Monarch at Sea Pines. This is a smaller resort compared to Barony Beach and Grand Ocean but it is right on the beach. It is located in Sea Pines Plantation, which in my opinion is a bonus in itself. The rooms have been recently redecorated and are definitely up to Marriott standards. We stayed last year in February and were given an ocean front room. We exchanged in through RCI and couldn't believe the excellent unit we were given. We love Hilton Head and go at this time every year. Hope you enjoy your visit. October is also an excellent time to visit Hilton Head. It is still warm enough to use the ocean and the weather is beautiful. We are also two older folks and this resort was perfect for us. Are you an RCI member. Not sure if II has Monarch in their inventory.

Some villas @ Marriott's Grande Ocean are ocean front examples the Sea Horse and the Sand Castle Villas.

Any time you are on The Island it is a great vacation.