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It seems to be a pattern for i-adjectives (in their "dictionary-form") to have low intonation on the first and last morae and high intonation in between, at least if they are three morae or more in length. Since forms like 帰らない and 帰りたい seem to convert verbs into i-adjectives, does the pitch accent follow? Going with the 帰る-example, is
[かえる]{HLL}
[かえらない]{LHHHL}
[かえりたい]{LHHHL}
correct?
Whilst there aren't many online resources for this sort of thing, there are very extensive paper resources. I highly recommend that you get either the NHK日本語発音アクセント辞典 or the 新明解日本語アクセント辞典 if you have questions beyond these two conjugations; you can figure out the tables even with very limited Japanese.
Essentially, 〜ない and 〜たい are actually separate words that attach to various stem forms of said verb (imperfective and continuative, respectively). Although they are separate units, they cannot be stand-alone words and are known as auxiliaries (助動詞). These auxiliaries conjugate differently to the verbs that they are attached to, which is why it seems to turn it into an adjective, as you put it.
There are a pretty limited number of pitch accent patterns for auxiliaries, but there is no way to know which pattern each follows without looking it up. Note that any pattern does not apply to conjugations of 〜ない and 〜たい, such as 〜なかった and 〜たかった, which have independent patterns and also can be looked up in these conjugation tables.
According to the NHK日本語発音アクセント辞典, where ○○ represents the verb stem and ●● represents the auxiliary:
There are various resources for finding the pitch accent of dictionary-form words, but it seems there aren't many for finding the pitch accent of inflected forms. The best I've been able to find is OJAD, the Online Japanese Accent Dictionary. Despite the English name, the site is put together by a Japanese organization, and the UI appears to be available in multiple languages.
Looking at their entry for 帰る, we see that the plain form pitch accent is かえる【HLL】. Meanwhile, the negative ～ない form pitch accent is かえらない【LHHLL】, as broccoli forest indicated in a comment. Following from that, the pitch accent for the past-tense ～なかった form is かえらなかった【LHHLLLL】.
Meanwhile, we see that the pitch accent for almost-homophonous 変える is different: plain かえる【LHH】, negative かえない【LHHH】, negative past かえなかった【LHHLLL】.
The OJAD dataset doesn't seem to include ～たい forms. My subjective impression is that these are similar to the ～ない forms, but I will certainly welcome any input from a native speaker. Darius Jahandarie points out that the ～たい form pitch accent for 帰る is かえりたい【LHHHL】, diverging from the negative.
