According to the National Index of Parish Registers there are transcripts of the MIs for 1790-1991 at Lincoln Reference Library and Lincolnshire Archives. However, this NIPR volume was published in 1995, so this might not still be the case.
The same transcript is apparently also at the Society of Genealogists in London, whose catalogue describes it as "Lincolnshire monumental inscriptions, vol. 43 [Typescript]" published by Lincolnshire FHS in 1993. So it's possible the society might have a copy at their research centre, even if they no longer have it for sale.