Try check out these websites. I hope it help. 

Is it possible to clarify the types of sex offender you are focusing on? (child molester, rapist, juvenile sex offenders, etc). Since each seem to have their unique assessments.

Cheer!

SiripornP.

http://csom.org/pubs/cap/2/2_0.htm

http://www.atsa.com/risk-assessment

http://www.static99.org/‎

http://www.online-testing.com/documents/SAI2/adult-juv-sai-chapter-handout.pdf‎‎

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www.smart.gov/pdfs/SexOffenderRiskAssessment.pdf‎

Please apologized for my previous answer, which I mistaken your question for sex offenders.

For victim's history of sex offender, I suggest this following paper (which included also self-report measure). Hope it helps, more or less. 

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Multiple perpetrator rape among girls evaluated at a hospital-based Child Advocacy Center: Seven years of reviewed cases ☆

Laurel Edinburgh a,Julie Pape-Blabolil aScott B. Harpin bElizabeth Saewyc c

‎,doi:‎10.1016/j.chiabu.2014.05.008

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http://www.sciencedirect.com/science/article/pii/S0145213414001847?via%3Dihub‎

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"...This questionnaire includes items and scales from the school-based Minnesota Student Survey (Minnesota Departments of Health and Education, 2007) that focused on health and risk behaviors, psychosocial contexts such as school and family relationships, self-esteem, and some limited socioeconomic status measures. The psychometric properties of these measures have been reported in other studies with adolescents generally, and with sexually abused adolescents specifically (Saewyc & Edinburgh, 2010). The assessment also includes the UCLA Post Traumatic Stress Disorder trauma checklist (Steinberg, Brymer, Decker, & Pynoos, 2004), and the Child Report of Parent Behaviors Inventory short 16-item version (CRPBI-16:Bosco, Renk, Dinger, Epstein, & Phares, 2003)..."‎

I cant offer a screening tool but interested in your looking at a link between CSA and GI disorders. When you say link are you thinking about medical or mental health consequences that result in GI symptomatology? There is a clear link between signs and symptoms in girls who experience genital touching primarily reflecting historical details that reflect trauma as a result of the sexual contact. There has been very little research regarding physical signs and symptoms of children who experience anal penetration or if your talking about the whole GI tract it could include oral trauma. Can you clarify what link your looking at?