The survivor notes appear throughout the map. Here's a handy-dandy list of where to find those notes.

Note #1: In one of the two buses
Note #2: Found in the area with the most houses, on either the table or one of the boarded up windows
Note #3: Underneath the Tower
Note #4: In one of the bunkers without a door

I recommend finding two notes that spawn relatively close to each other or close to the locked bunker (a bus is nearby it).

For those who are new playing this game, the locked bunker can be found if you go east from the start point, and continue down the road until it ends. Once you reach the end, turn east again and continue walking, and you will eventually find the bunker.

If you had to hide from Siren Head while heading to the bunker, then check the digits on the two notes you collected. Remember what placement the digits have.

By now, you should know the digits of the two notes you have collected and the placements of those digits. This next part might be a bit confusing, so be prepared.

In order to unlock the bunker with two notes, this step is crucial. Interact with the bunker door to get the digit input screen. Once you have that, enter the digits you have already and fill in the blanks with 0, and keep going up until the door unlocks.

Example: You have collected notes #2 and #4. The digit for note #2 is 2, and the digit for note #4 is 6.
You would input the code like this:
0206
If that fails, keep going up, like so.
0216
0226
0236
0246
0256
0266
0276
0286
0296
Once you have done digits 0-9, move up the first number to the next digit:
1206
1216
1226
1236
1246
1256
1266
1276
1286
1296
Lets say the door code is 3246. You would reach this code in 45 attempts, which goes quickly depending on how fast of a typer you are.

Caution: This section contains minor spoilers for the game.

Granted, it is easier to enter the code when you have all four notes. But, Siren head becomes more aggressive with the more items you collect. By collecting only half of the notes you need, Siren Head will be less aggressive and is less likely to teleport directly in front of you.

This allows you to get the secret ending involving the matches with only collecting 4 items instead of 6-7 items, thus making getting across the map from the bunker to the gas station easier since Siren Head will be less aggressive.

I've done this strategy before, and it helped me get the secret ending.

I hope this strategy has helped you like it helped me. When the devs fix the teleportation bug this guide will become less relevant, but that should be a while.

Comment if you have suggestions for this strategy, and good luck!