Ultron appears in two flashbacks in IM3 47 (one of them -BTS), so we need some page citations.
The Sons of Yinsen find the “Sentient Armor” (actually Ultron): (5-6:5)
The “Sentient Armor” attacks Jocasta: (14-15:5)
ULTRON
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IM3 29 (4:1 - 9)-FB-BTS
*IM3 47 (14-15:5)-FB-BTS
NW2 9-BTS
IM3 29 (10 - 18)-FB-BTS
IM3 29-BTS
IM3 30-BTS
IM '00-BTS
*IM3 47 (5-6:5)-FB
IM3 48-FB
…