Pathfinder 1E How can one add tentacle attacks to a natural attack routine?

I was going for a natural attack build and was trying to see if there is a way to add tentacles to it.

The alchemist has a tentacle discovery but that explicitly says that it doesn't add to the number of attacks per round (I guess it replaces an existing attack?).

There is the tentacle cloak for a 1/day thing.

What else is out there in pathfinder rules (not 3rd party, alas)?

Assuming you are willing/allowed to take a 1 level dip into Summoner - Synthesist you can evolve tentacles (1d4+half Str/secondary attack). Your best option is to select the Biped form, which giving you 2 claw (1d4+Str/primary attack) attacks for free. Unfortunately, first level limits you to possessing a maximum of 3 natural attack evolutions, but a reasonable DM would allow you to exchange the claws for the weaker tentacles that have a -5 to BAB when attacking. Either way, you will be only spending 1 evolution point on a tentacle. The other 2 would be best spent on increasing the tentacle(s) to d6s and gaining +2 natural armor.

Don't forget that primary natural attacks uses full attack bonus and secondary ones are full attack bonus -5. In addition, if you make a weapon attack, all natural attacks are treated as secondary attacks. Assuming you have a bonus of +9/4 and 3 tentacles, your full attack would look like: +9 weapon, +4 weapon, +4 tentacle 1, +4 tentacle 2, +4 tentacle 3.

Cons:
* Lose at least 1 level of alchemist progression.
* While melded with the eidolon, your Str, Dex and Con are replaced with your selected form. The Biped is 16/12/13 for first level. These changes affect all rolls that are dependent upon 1 of those attributes. (Skills/Saves/etc)
* While melded with the eidolon, you "lose" your armor and gain it's natural armor instead. The biped has an natural armor of 2.
* Selecting any base form other than Biped will require you to spend 2 of your evolution points on arms. Otherwise you will be unable to cast spells, throw bombs, etc.

Pros:
* While melded with the eidolon, you gain a bunch of temp HP.
* Mutagens still work if consumed after melding with the eidolon.
* While melded with the eidolon, you gain Darkvision 60ft at level 1 and Evasion at levle 2.
* All magic items, other than you armor, continue to function while melded.
* Access to a handful of spells and cantrips.
* While not melded with the eidolon, 3+Cha use per day of Summon "trap checker/heavy lifer/scout" Monster that lasts 1 min per level.