How to reach Telok Penjarah to buy the Padewakang blueprint
As you can see on the map above, Telok Penjarah is leagues northeast of Sainte-Anne. Worse, you also have to Skull and Bones Items cross open waters. That means storms, choppy seas, and rogue waves that can instantly destroy your ship if you don't brace properly. Here are some tips:

Don't bother sailing along a straightforward course from Sainte-Anne to Telok Penjarah since the stormy seas will be tough to navigate.
Instead, we recommend island-hopping by way of Lanitra (Red Isle) -> Moyenne Crique (L'Escale) -> Three Brothers (Eastern Basin) -> Return Fleet Bight (Eastern Basin) -> Parujar's Cry (Zamrud) -> Telok Penjarah.
The reason for this is so you only need to cross short distances in between each outpost. You also end up tagging additional fast travel points to help you along the way.
Once you arrive in Telok Penjarah, look for the Shipwright NPC. If you've already reached Brigand rank, you can buy the Padewakang blueprint for 5,280 silver.

Padewakang crafting requirements
The Skull and Bones Padewakang ship requires the following crafting materials:

18x Ironwood Plank - Can be purchased from Subu Lumberyard, Kencur Lumberyard, and Suny Lumberyard.
15x Steel Ingot - Can be purchased from South Damai Foundry and Kota Lama Foundry.
15x Fine Ramie - Can be purchased from Kencur Weaver and South Suny Weaver.
4x Shellac - Can be purchased from Suny Capital, as well as other village settlements (i.e. Kencur, Kota Lama, and the like).
4x Crude Saltpeter - Obtained from ships plying the trade routes in the East Indies.
2,880 silver
Note that you may also gather raw materials (i.e. Ironwood, Pure Iron, and Ramie) from resource nodes in the region. The Dutch and Rempah ships that you destroy might also have these items. It's really up to you if you want to Skull and Bones Items for sale farm them normally, or if you just want to spend silver to buy stuff.