Question: I am trying to learn about pitch accent, and I have heard that there are rules for suffixes regarding pitch accent. Are there any resources where I could learn about those rules ?

I am not yet able able to really understand all in Japanese sources, which may be why I have been unlucky with finding out more about it.

I know about [ojad](http://www.gavo.t.u-tokyo.ac.jp/ojad/eng/pages/home), [weblio](https://www.weblio.jp/) and [u-biq](https://accent.u-biq.org/) which can be useful for looking up individual words of even counters in the case of the last one ; however I have yet to come across a place where I can learn about rules and suffixes.
I'd be grateful if anyone could tell me how or where I can learn them !

by suffixes I mean things like 方、屋、的 or even counters such as 日、つ、or　個.

*ps : if you have any other useful resource for pitch accent than the ones I have cited, even unrelated to suffixes, please feel free to share them as well !*

Answer: 
The NHK Accent Dictionary contains a section on compound words, which has entries such as 〜体、〜生、〜力 etc. that explains the pattern they use for connecting to the previous word. It also has a very detailed appendix of how compound words work in general.

It doesn't have any compound entries for things like 〜ぽい or 〜さ, but there are many full entries like 荒っぽい、安っぽい etc. that you can use to determine the pattern yourself.

If you are asking about 助動詞 like たら、たい、し etc, then the appendix covers that.

As for counters, there is a separate section of the dictionary for them, which for each counter, covers all accents from 1 to 100, as well as 1000 and 10000.

The NHK Accent Dictionary is available in print and on iOS via the MONOKAKIDO Dictionaries app.
Regarding counters there are no rules in general. But some kinds of counters are more or less predictable.

1. One mora counters

One mora counters are preaccented in general: 個,里,羽 etc (一個 [Ikko],一羽 [ICHIwa]...). One useful exception is 度 [do] when used as 'times', though it's also preaccented when used as 'degrees'

2. Three or more mora counters

Three or more mora counters of western origin adhere to -3 rule most of the time: 一センチ [ISSEnchi],一グラム [ICHIGUramu],　一メートル [ICHIMEetoru].

Three or more mora compound counters can have different pitch patterns, but they are usually consistent regardless of preceding number. Thus, ~番線 is always unaccented, ~時間 always has a pitch drop right before [kan] etc.

3. Two mora counters

Two mora one kanji counters of western or Japanese origin are mostly preaccented: キロ,ミリ,組,皿 ([ICHIkiro],[HITOsara]...).

Two mora one kanji counters of Chinese origin are the most unpredictable. I counted about 17 different patterns. Keep in mind, that they might have different pitch accent with different numbers and different variations of numbers (二台 is accented, but 五台 is not; [nin] in 八人[HACHInin] is preaccented , but is accented in 九人 [KUNIn] (though it becomes 頭高 when pronounced as [KYUunin])).
The only more or less predictable situation is when the counter consists of two short syllables (no moraic ん, no long vowel, no あい diphtong), and there's a gemination between the number and first mora of counter (一曲 [ikkyoku], 八冊 [hassatsu] etc) - in this case the whole word tend to be post-accented (尾高 pattern).