Where does the phrase だらけ come from? I only know だ as a copula and ら as a conditional marker or pluralizing suffix, are either of these at use in this phrase? My dictionary lists it as "implying (negatively) that something is full of".
As far as I know, there is no consensus for the origin of this word. I've checked a number of resources including 日本国語大辞典 (but the 精選版, not the full edition), 日本文法大辞典, and the other various monolingual dictionaries I have at hand, and none offer an explanation.
Martin offers one theory, courtesy of Ōtsuki, on page 136 of his 1975 Reference Grammar of Japanese, where he discusses the etymology of several words including だらけ. First he notes:
Where do these words come from? Many of those with distinctively voiced initials go back to elements with voiceless initials, having picked up the voicing as part of the well-known compound nigori process. The restrictive だけ is from the noun たけ 'length; total quantity', related to たか 'amount, volume' and たか- 'high, tall' (as is たけ 'peak').
He gives a number of other examples that fit this pattern, then discusses だらけ very briefly:
The origin of だらけ is problematical; one suggestion (Ōtsuki) has it related to たらたら 'dripping profusely'.
I don't know if you'll find this information satisfying, but it's all I can dig up at the moment. Perhaps someone else will have something to add.