Yes, the pattern “because of which” exists and is legitimate usage in English grammar. It means “on account of which,” as in this sentence: “I regret reading that horror novel, because of which I hardly slept last night.” Note that the comma before the subordinate clause is a must in such constructions in the same way as in its equivalent sentence using “on account of which”: “I regret reading that horror novel, on account of which I hardly slept last night.”
Without that comma, both "because of which" and "on account of which" constructions become dysfunctional, turning into run-on sentences:
“I regret reading that horror novel because of which I hardly slept last night.”
“I regret reading that horror novel on account of which I hardly slept last night.”