Is it really the diacritic you are interested in, or are you looking for words that differ only in tone (and if so, does it matter whether the spoken tone differs from the written tone)?
Maybe have a look at these examples:
สู้ to fight
สู่ preposition (in)to
เสื้อ shirt / blouse
These word sets differ only in the diacritic / tone. As you can see the second set contains three words - I'm not sure how literally to take 'pair'. There are five tones, so there will be a few cases where you have more than two words differing only in tone.
Here there is an additional difference in that a different character is used for the vowel (it's the same vowel though).
มา to come
Here the ห is silent - it acts like a diacritic in that it forces a rising tone, but it's not really a diacritic. You might need to decide whether to count it. The same thing can happen where the written forms differ in that one uses a high class consonant while the other uses a low class equivalent, e.g:
คาว to smell bad
ข and ค have the same pronunciation (kh) but ข is a high class consonant (resulting in a rising tone in this example) whereas ค is a low class consonant (resulting in a mid tone in this example). IOW the spoken forms differ only in tone, but you can't really say that the written forms differ only in terms of diacritics.
I'm assuming that the diacritics you have in mind relate to tone (bearing in mind the example you gave) but be aware that there are other diacritics, notably one used to shorten some vowels.
Edit: thanks for your comment.
It looks like you are not counting pairs of words with different diacritics but are looking for one with and one without, so not counting the first pair I suggested.
I haven't come across a list of words like that, but you could try the forums at thai-language.com and thaivisa.com. You can join thaivisa.com easily enough and ask there. Those guys are mainly western expats living in Thailand. If posting I would use the term 'tone marker' - or maybe just ask for a list of words that differ only in tone. You would then need to check the spellings to confirm that they are the same except that one has a diacritic - this is by no means guaranteed.
On the assumption that you need one word not to have a diacritic, you have 2 or 3 above (depending on whether you use เสือ twice) - how many do you need?
Some others that occur to me are:
ตัว body (the squiggle on top is a vowel, not a diacritic - same for เสือ above)
เขา third person pronoun (written with rising tone, pronounced with high tone)
เข้า to enter (written and pronounced with falling tone)
วาง to set something down
ว่าง to be free (i.e. not busy, of a person; vacant, of a building plot etc - unoccupied)
เดียว single (just one) again the squiggle over the second character is part of the vowel, not a diacritic
เดี๋ยว (in a) moment