The challenge to this subset is not finding the variations because they are reasonably easy to locate on EBay, Sportslot or Beckett. The challenge is finding the home runs that one needs for a reasonable price. It would seem that most of the numbers can be purchased for $3.00 or $5.00 including shipping. At this price it would cost about $300 to $350 to complete a set. But I have seen these cards listed for $6.00 to $10.00 (and higher).
The cards that I have just added are home runs #4 and #53. Sosa hit home run #4 on April 23, 1998 off of Dan Miceli of the Padres. This was before Sosa's big June home run explosion. After this home run, he was on track to hit a season total of 37 HRs.
Home run number 53 came on August 28, 1998 against the Rockies. The pitcher was John Thomson. This home run tightened the race between McGwire and Sosa to just a single HR.
The 15 cards that I still need to complete this HR Parade sub-set are; 9, 14, 16, 18, 19, 22, 23, 26, 29, 37, 38, 42, 52, 55 and 61.