Times Cryptic 28,026

[NeilMunro]

Very grateful for all help with these clues please.
17dn: “Tacky bloke reportedly on addictive drug (8).”
19dn: “Neptune’s satellite’s interval discharging energy (6).”
23ac: “National firm once caught importing large antelope (9).”
24dn: “Thickhead finally sacked by boss (5).”
28ac: “Waller starts to take on cattle, keeping animals for slaughter (8).”

[Lie-in King]

17d Gimcrack (tacky) - "Jim" (reportedly) + 'crack' (drug)
19d Triton - 'tritone' (interval, discharging 'e[nergy]')
23a Icelandic - 'ICI (firm once) c(aught)' (importing) 'eland'
24d Dumbo - '(sacke)d' (finally) + 'umbo' (boss; centre of a shield)
28a Fatstock - 'Fats' (Waller) + 't(ake) o(n) c(attle) k(eeping)' (starts)

[elliemay1]

17 gimcrack

[NeilMunro]

Many thanks Lie-in King!!!

[HardTimes]

It could be "Jimcrack" which is a variant of "Gimcrack".