Others have provided more specific answers already, but regarding mimetic adverbs, like ぞくりと and ばしゃんと, you might like to know that there are a few general and somewhat productive (=people use them more or less freely to coin new words) heuristics at play, which kind of explains why you don’t find them in dictionaries.
Mimetic words usually consist of some kind of stem, which is usually two mora-long, ぞく, ばしゃ, etc. + some fluff. Fluff comes in a few regular varieties and some outliers which are not really productive (= should be in dictionary).
- You may double the sound if it’s two-mora long, ぞく → ぞくぞく, and then optionally add と or っと
- You may pad with り/ん/っ and then add と (not optional)
- Advanced tip: you may swap vowels because you think it sounds better that way. U/o sometimes swap, depending on speaker preferences, if the second mora has a subdued vowel (e.g., ku pronounced as k’) it could probably also swap between i/u, I believe, etc.
What this means for you as a reader is that, if you find some mimetic word that is not in your dictionary, one thing you can do (besides searching the web, asking natives, etc.), is apply the above rules in reverse to try to guess some other form that would be in the dictionary. For example, here, zokurito = zoku (stem) + rito (fluff), so you try zokuzoku for example and jmdict / jisho has it. Same with bashanto = basha + nto, and you guess bashatto
Addendum about fluff
The fluff actually isn’t meaningless. In case you care, quoting from Hamano (hiragana mine):
/N/ (ん) indicates that the action involves elastic objects or is accompanied by a reverberation.
/Q/ (っ) on the other hand indicates that the movement is carried out forcefully or vigorously in a single direction.
/-ri/ (り) […] indicates ‘quiet ending of the movement.’