I only see the りんご reading in iwanami dictionaries (iwakoku, koj). Iwakoku has it marked as a jukujikun.

Shinmeikai prefers the ひょうか reading, so I placed that one first. Daijisen gives equal weight to へいか and ひょうか.

Most of the refs are pretty explicit that this refers only to the fruit. 「リンゴの果実。」

smk: リンゴの、業界用語。
Given the relative rarity of this form, I think a [rare] tag might be appropriate.

Google N-gram Corpus Counts
╭─ーーー─┬───────────┬───────╮
│ 苹果　 │     6,495 │  0.1% │
│ りんご │ 4,435,078 │ 58.0% │
│ 林檎　 │ 1,204,319 │ 15.7% │
│ リンゴ │ 2,005,099 │ 26.2% │
╰─ーーー─┴───────────┴───────╯

Proposed split from 1555480