I would need influencers to evaluate if a brand fits with them for a collaboration. Does anyone know where could I find a suitable scale/items for this?
If I understand correctly you want to measure the perceived fit between influencers and brands. There are several directions you could take depending on your theoretical conceptualization of the construct (fit) you're intending to measure, such as brand identification (identity as determinant), person–organization fit (value congruence as determinant), or compatibility/similarity. Here are some references that might be helpful:
Brand Identification
Lam, S. K., Ahearne, M., Mullins, R., Hayati, B., & Schillewaert, N. (2013). Exploring the dynamics of antecedents to consumer–brand identification with a new brand. Journal of the Academy of Marketing Science, 41(2), 234–252. https://doi.org/10.1007/s11747-012-0301-x
Levinger, G. (1980). Toward the Analysis of Close Relationships. Journal of Experimental Social Psychology, 16(6), 510–544. https://doi.org/10.1016/0022-1031(80)90056-6
Mael, F., & Ashforth, B. E. (1992). Alumni and their alma mater: A partial test of the reformulated model of organizational identification. Journal of Organizational Behavior, 13(2), 103–123. https://doi.org/10.1002/job.4030130202
Wolter, Jeremy S. and J. Joseph Cronin Jr. (2016), "Re-Conceptualizing Cognitive and Affective Customer–Company Identification: The Role of Self-Motives and Different Customer-Based Outcomes," Journal of the Academy of Marketing Science, 44 (3), 397-413.
Person–Organization Fit
Cable, D. M., & DeRue, D. S. (2002). The convergent and discriminant validity of subjective fit perceptions. Journal of Applied Psychology, 87(5), 875–884. https://doi.org/10.1037//0021-9010.87.5.875
Jensen, U. T., Andersen, L. B., & Jacobsen, C. B. (2019). Only When We Agree! How Value Congruence Moderates the Impact of Goal‐Oriented Leadership on Public Service Motivation. Public Administration Review, 79(1), 12–24. https://doi.org/10.1111/puar.13008
Judge, T. A., & Cable, D. M. (1997). Applicant Personality, Organizational Culture, and Organization Attraction. Personnel Psychology, 50(2), 359–394. https://doi.org/10.1111/j.1744-6570.1997.tb00912.x
Roberson, Q. M., Collins, C. J., & Oreg, S. (2005). The Effects Of Recruitment Message Specificity On Applicant Attraction To Organizations. Journal of Business and Psychology, 19(3), 319–339. https://doi.org/10.1007/s10869-004-2231-1
Compatibility/Similarity
Packard, Grant, Andrew D. Gershoff, and David B. Wooten (2016), "When Boastful Word of Mouth Helps versus Hurts Social Perceptions and Persuasion," Journal of Consumer Research, 43 (1), 26-43.
Trimble, C. S., & Rifon, N. J. (2006). Consumer perceptions of compatibility in cause-related marketing messages. International Journal of Nonprofit and Voluntary Sector Marketing, 11(1), 29–47. https://doi.org/10.1002/nvsm.42