I'm currently reading "Amazing Spider-Man: The Original Clone Saga" TPB which collects ASM #'s 139-150, Giant-Size Spider-Man #5, and Peter Parker, The Spectacular Spider-Man #'s 25-31, 149, 162-163, & Annual #8. The books states that Gwen's death was in ASM #'s 121-122, the making of the Spider-Mobile in #126, and Marvel wikia says the first appearance of the Punisher Was #129. Please LMK if there's a TPB or something that collects these.
To get those 4 specific issues in one volume? Essential Amazing Spider-Man Vol. 6. There are plenty of reprints of ASM 121 & 122. There's a True Believers reprint of ASM 129, nice and cheap. ASM 126 probably hasn't been reprinted that much.