Shiva Purana
शतादिकसहस्रस्य विधिरेष प्रकीर्तितः । तदभावे प्रकारोन्यः शुभः संप्रोच्यते मया ३३ ।
This is the rule regarding eleven hundred Rudrākṣas. If so many are not available, another auspicious procedure I mention to you.
english translation
zatAdikasahasrasya vidhireSa prakIrtitaH । tadabhAve prakAronyaH zubhaH saMprocyate mayA 33 ।
hk transliteration by Sanscript