I think 果が行く can be search-only.
中辞典 has this under its 捗/はか entry. I think the previous xref is better.

@@ -11,0 +12 @@
+<ke_inf>&sK;</ke_inf>
@@ -22 +23 @@
-<xref type="see" seq="1430570">捗る</xref>
+<xref type="see" seq="2817380">捗</xref>

はかが行く	83	0.1%
はかがいく	133	0.1%
はかがゆく	34	0.0%
捗が行く	0	0.0%
捗がいく	0	0.0%
はかどる	129523	88.8%
捗る	16093	11.0%

Good explanation of farming etymology, also equates to 捗る
https://www.fleapedia.com/五十音インデックス/は/はかが行く-捗が行くとは何か/
「はかどる（捗る）」も同じ意味。

I agree with previous comments (and current glosses) that these terms are essentially synonymous. 

Given the comparative rarity of this structure, and commonness of the xref, I think it's more helpful to mark [rare] and link to the synonym, than to link to 捗 to help piecemeal-construct the meaning of  捗が + 行く.

The kanji forms are quite rare indeed.  sankoku does not list kanji for はか (though it gives はかがいく as the example), and neither does daijs.

Nikk gives only はか【果】 が 行(ゆ・い)く, for which there is no ngram support at all. 

You basically can't find 捗が行く or 果が行く with kanji on the general internet, but they do turn up in some old google books results. 

daijs gives いく and ゆく. nikk gives only ゆく.  ngrams give いく
はかがいかない	235	  
はかがいきませ	52

Not sure I've met a word where it was considered impermissible for 行く to be read as いく. In any case, Nikk secondarily supports いく as legitimate, at least. Sankoku lists ambiguously in kanji 行く form.

@@ -9,0 +10,6 @@
+<k_ele>
+<keb>果が行く</keb>
+</k_ele>
+<r_ele>
+<reb>はかがいく</reb>
+</r_ele>
@@ -16 +22,3 @@
-<xref type="see" seq="2817380">捗・はか</xref>
+<xref type="see" seq="1430570">捗る</xref>
+<misc>&uk;</misc>
+<misc>&rare;</misc>

Ngrams. GG5, etc. in 捗/捗る entries.

@@ -3,0 +4,3 @@
+<k_ele>
+<keb>はかが行く</keb>
+</k_ele>
@@ -12,0 +16 @@
+<xref type="see" seq="2817380">捗・はか</xref>

daijr
Luminous (捗 entry, points to はかどる)

Maybe a xref to 捗る?